pthread_create: Fix an (unlikely) error in fallback value in the event of a failure (which should never occur)

TCB: Increase the size of the scheduling policy field from 1 to 2 bits to allow additional, planned scheduling policies

Add CONFIG_NETDEV_LATEINIT that can be used to suppress calls to up_netinitialize() from early initialization

- Rename include/nuttx/net/dnsclient.h to dns.h
- Move internal DNS prototypes from dns.h to libc/netdb/lib_dns.h
- Global standard DNS definitions from libc/netdb/dns_soccket.c to dns.h
- Eliminate dns_gethostip().  This is now an internal part of gethostbyname()
- Eliminate interface dns_whois().  Not needed in this new context.

arch/arm/src/sama5/sam_ehci.c:  Fix some bad conditional compilation that left a function undefined if CONFIG_USBHOST_ASYNCH is not selected.

tools/testbuild.sh:  Add a script that can be used perform test builds on a set of board configurations

Fix references to the no-longer-existent misc/ directory in comments, README files, and documentation