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

Fix several compile errors for logic added for CONFIG_BUILD_KERNEL, but which cause problems for other configurations

Space at the beginning of the process data space is now reserved for user heap management structures.  In the kernel build mode, these heap structures are shared between the kernel and use code in order to allocate user-specific data.

Fix error in initialize of IDLE TCB due to last change.  The argument list is no long in the TCB, but in the stack.  But not for the IDLE task.  It needs its own mini-argv[] list so that it looks more like other threads.

There used to be two ways to pass parameters to new tasks, depending upon the configuration:  Either (1) argv[] as created as an array with each string strdup'ed.  Or (1) argv[] array and strings were created on the stack before the new task was started.   Now, there is only one way, way (1).  Way (2) might be slightly more compact, but this is not worth carry the complexity of two different ways of doing the same thing.