sched/:  Fix several inappropriate accesses to get_errno() that were missed in previous changes (some going back to nuttx-.23).  Add new nxsched_setscheduler() and nxsched_getaffinity() which are equivalent to their counterparts without the nx on front.  These versions do not modify the errno value.  Changed all calls within the OS to use these newer versions of the functions.

    sched/sched:  Correct some build issues introduced by last set of changes.
    sched/sched:  Add new internal OS function nxsched_setaffinity() that is identical to sched_isetaffinity() except that it does not modify the errno value.  All usage of sched_setaffinity() within the OS is replaced with nxsched_setaffinity().
    sched/sched:  Internal functions sched_reprioritize() and sched_setpriority() no longer movidify the errno value.  Also renamed to nxsched_reprioritize() and sched_setpriority().
    sched/sched:  Add new internal OS function nxsched_getscheduler() that is identical to sched_getscheduler() except that it does not modify the errno value.  All usage of sched_getscheduler() within the OS is replaced with nxsched_getscheduler().
    sched/sched:  Add new internal OS function nxsched_setparam() that is identical to sched_setparam() except that it does not modify the errno value.  All usage of sched_setparam() within the OS is replaced with nxsched_setparam().
    sched/sched:  Add new internal OS function nxsched_getparam() that is identical to sched_getparam() except that it does not modify the errno value (actually, the previous value erroneously neglected to set the errno value to begin with, but this fixes both issues).  All usage of sched_getparam() within the OS is replaced with nxsched_getparam().

net/udp:  Fix memory leak with UDP + write buffer is closed.  Also update TODO and comments and refresh a configuration.

net/tcp:  Write buffering logic should not wait for a free buffer if the socket was opened non-blocking.  Also, rename the TCP write buffering macros from WRB_* to TCPWB_* to make room in the namespace for write buffering with other protocols.

net/udp:  Fix memory leak with UDP + write buffer is closed.  Also update TODO and comments and refresh a configuration.

net/tcp:  Write buffering logic should not wait for a free buffer if the socket was opened non-blocking.  Also, rename the TCP write buffering macros from WRB_* to TCPWB_* to make room in the namespace for write buffering with other protocols.

    fs: Add truncate() support for userfs
    fs/unionfs:  Add truncate() support to the unionfs
    fs/tmpfs:  Add ftruncate() support to tmpfs
    syscall/: Add system call support for ftruncate()
    net/route:  Adding ftruncate() support eliminates an issue in file-based routing table management.
    fs:  Add basic framework to support truncate() and ftruncate().  The infrastructure is complete.  Now, however, the actual implementation of ftruncate() will have to be done for each file system.

arch/arm/src/stm32/stm32f33xx_adc.c:  Eliminate warnings about cj_channels and j_chanlist being set but not used.

sched/signal/sig_nanosleep.c and libc/time/lib_nanosleep.c:  Implement clock_nanosleep().  nanosleep() is now reduced to a libc wrapper around clock_nanosleep().

This comment converts the underlying IPC used by the UserFS from Unix domain local sockets to UDP LocalHost loopback sockets.  The problem with the local sockets is that they do require operations on the top level psuedo-file system inode tree.  That tree must be locked during certain traversals such as enumerate mountpoints or enumerating directory entries.

This conversion is unfortunate in the sense that Unix local domain sockets are relatively lightweight.  LocalHost UDP sockets are much heavier weight since they rely on the full UDP stack.  If anyone is up for a complete redesign, then using some shared memory and a POSIX message queue would be lightweight again.

This commit also fixes several bugs that were not testable before the inode tree deadlock.  I cannot say that the logic is 100% stable but it does not have basic functionality.

Squashed commit of the following:

    fs/userfs:  Order locking so that access to the shared I/O buffer is also locked.
    fs/userfs:  Converts to use LocalHost UDP loopback for IPC.

Kconfigs: Add CONFIG_LCD_UPDATE that works like CONFIG_NX_UPDATE but can be enabled without enabling the graphics subsystem.

drivers/loop: Don't use file descriptors... Use the internal file system interfaces so that the loop device can be shared across threads.

fs/userfs:  There are some deadlock issues that make the UserFS un-usable at the current time.  Added to the TODO list; also feature is now marked EXPERIMENTAL.

Update TODO for broken local socket feature; Add work around to UserFS for broken local socket feature.

drivers/net:  Remove the old, unfinished Crystal LAN driver.  I don't even have the hardware that it goes with anymore.

    fs/mount:  Implements procfs /proc/fs/blocks and /proc/fs/usage files, replacing the NSH df command.
    fs/mount:  Implements procfs /proc/fs/mount file, replacing the NSH mount command when there are not arguments.
    fs/: Move prototype of foreach_mountpoint out of include/nuttx/fs/fs.h to fs/mount/mount.h.  Add framework for the mount procfs (initial commit is just a close of the net/route table procfs.

This commit adds support for semi-standard IPPROTO_ICMP6 sockets.  This is a replacement for the non-standard ICMPv6 ping support that violated the portable POSIX OS interface.

Squashed commit of the following:

    net/icmpv6: IPPROT_ICMP6 socket logic now builds without error.
    net/icmpv6:  Add support for read-ahead and poll(). Initial commit is just cloned from ICMP with the appropriate name changes.
    configs/:  All defconfig filess that include CONFIG_NET_ICMPv6_SOCKET=y need to select CONFIG_SYSTEM_PING6=y and deselect CONFIG_DISABLE_POLL.
    Update NSH documention to show that ping6 is now a built in command.
    net/icmpv6:  Add icmpv6_sendto.c and icmpv6_recvfrom.c.  Initial versions are just clones from icmp/ with appropriate name changes.
    net/icmpv6:  Clone some ICMP socket logic as the beginning of support for ICMPv6 socket support.
    Rename CONFIG_NET_ICMPv6_PING to CONFIG_NET_ICMPv6_SOCKET.  Move prototype for icmpv6_ping from include/nuttx/net/icmpv6 to net/icmpv6/icmpv6.h

This change adds support for semi-standard IPPROTO_ICMP AF_INET datagram sockets.  This replaces the old ad hoc, nonstandard way of implementing ping with a more standard, socket interface.

Squashed commit of the following:

    net/icmp:  Finishes off icmp_recvfrom().
    net/icmp:  Add readahead support for IPPROTO_ICMP sockets.
    net/icmp:  Add poll() support for IPPROTO_ICMP sockets.
    net/icmp:  Add a connection structure for IPPROTO_ICMP sockets.
    net/icmp:  Implements sendto for the IPPROTO_ICMP socket.
    net/icmp:  Move icmp_sendto() and icmp_recvfrom() to separate files.  They are likely to be complex (when they are implemented).
    net/icmp:  Hook IPPROTO_ICMP sockets into network.  Fix some naming collisions.  Still missing basic ICMP send/receive logic.
    configs: apps/system/ping current need poll() enabled.
    configs: All defconfig files that use to enable low-level support must now enabled CONFIG_SYSTEM_PING.
    net/icmp:  Adds basic build framework to support IPPROTO_ICMP sockets.

    fs/fat:  Remove mkfatfs from the OS.  This is a user-space application and belongs in apps, not in the OS.

kthread_create():  Rename kernel_thread() to kthread_create() for better naming consistency with task_create() and kthread_delete().