Squashed commit of the following:

This commit backs out most of commit b4747286b1.  That change was added because sem_wait() would sometimes cause cancellation points inappropriated.  But with these recent changes, nxsem_wait() is used instead and it is not a cancellation point.

    In the OS, all calls to sem_wait() changed to nxsem_wait().  nxsem_wait() does not return errors via errno so each place where nxsem_wait() is now called must not examine the errno variable.

    In all OS functions (not libraries), change sem_wait() to nxsem_wait().  This will prevent the OS from creating bogus cancellation points and from modifying the per-task errno variable.

    sched/semaphore:  Add the function nxsem_wait().  This is a new internal OS interface.  It is functionally equivalent to sem_wait() except that (1) it is not a cancellation point, and (2) it does not set the per-thread errno value on return.

fs/semaphore/sem_open.c

@@ -70,7 +70,7 @@
  *   task.  Following a call to sem_open() with the semaphore name, the task
  *   may reference the semaphore associated with name using the address
  *   returned by this call.  The semaphore may be used in subsequent calls
- *   to sem_wait(), sem_trywait(), and sem_post().  The semaphore remains
+ *   to nxsem_wait(), sem_trywait(), and sem_post().  The semaphore remains
  *   usable until the semaphore is closed by a successful call to sem_close().
  *
  *   If a task makes multiple calls to sem_open() with the same name, then