Fix some conditional compilation in kernel build mode.  And, while we are touching this logic, make g_default_pthread_attr const.

Remove the 16z board support from the main source tree.  It is still avaialable in the misc/Obsoleted directory

Beginning of logic that will, hopefully, all me to build applications against a NuttX export package (vs. the nuttx/ source tree).

The 'make export' target needs to bundle up the user C startup file (crt0), not the kernel head object

Fix 'make export'.  Adding subdirectories to the sched/ directory broke the header file collection logic

Fix more places where the user-mode allocator is used to allocate kernel thread resources -- before the user-mode allocator even exists

Group creation logic must use new group flag when allocating resources so that the privileges on the resource are set correctly

Add a flag to group structure:  If the group is created by a kernel thread, then all resources in the group must be priviliged