Add support for a per-process virtual page allocator.  This is a new member of the task_group_s structure.  The allocaor must be initialized when a new user process is started and uninitialize when the process group is finally destroyed.  It is used by shmat() and shmdt() to pick the virtual address onto which to map the shared physical memory.

Fix a few compile bugs and minor corrections to the mikroe-stm32f4 configuration source.  From Ken Pettit

procfs:  Fix some breakage introduced by reorganizing some un-reorganizable data structures.  From Ken Pettit