Add simulator configuration for testing the Union Fs.  Fix a few bugs.  Almost works but still too flaky

Add support for a union file system that can be used to overlay and merge the content of two mounted file systems.

POSIX message queues:  Move mq_setattr() and mq_getattr() from nuttx/libc/mqueue to nuttx/sched/mqueue.  Also add sysyscall support for mq_setattr() and mq_getattr().  This is necessary in protected and kernel builds because in those cases the message queue structure is protect and cannot be accessed directly from user mode code.  Noted by Jouko Holopainen.

Networking:  Modify how callback structures are stored to avoid another potential use of a stal pointer.

mq_timedreceive() move the location where the errno value is set; the TIMEDOUT errno setting was being overwritten by subsequent actions before returning.  Noted by Freddie Chopin.

Extend the mkconfig tool so that it can dequote a quoated list of quoated strings.  THTTPD uses such a configration setting to provide the list of index files.

Damn.  THTTPD will not yet run with binfs because it wants an index.html file.  THTTPD does support indexing directories if CONFIG_THTTPD_GENERATE_INDICES=y, but there are some compilation issues that need to be fixed when that option is selected.

Olimex LPC1766STK.  Add an example configuration showing how to build apps/netutils/thttpd using binfs