Move sleep() and usleep() from sched/ to libc/unistd/.  These functions now are simple wrappers for nanosleep().  Remove sleep() and usleep() from system calls; add nanosleep() to system calls

strftime should also return zero if the resulting string is truncated and/or not properly NUL terminated

libc logic should not directly assign errno, but should use set_errno() macro.  This is because in the kernel build, errno is a system call

Add board support infrastructure for the pcDuino board.  There is not much there on the initial checkin