This commit renames all internal OS functions defined under sched/task so that they begin with the prefix. For example, nxtask_exit() vs. task_exit().

Squashed commit of the following:

    Trivial, cosmetic
    sched/, arch/, and include:  Rename task_vforkstart() as nxtask_vforkstart()
    sched/, arch/, and include:  Rename task_vforkabort() as nxtask_vforkabort()
    sched/, arch/, and include:  Rename task_vforksetup() as nxtask_vfork_setup()
    sched/:  Rename notify_cancellation() as nxnotify_cancellation()
    sched/:  Rename task_recover() to nxtask_recover()
    sched/task, sched/pthread/, Documentation/:  Rename task_argsetup() and task_terminate() to nxtask_argsetup() and nxtask_terminate(), respectively.
    sched/task:  Rename task_schedsetup() to nxtask_schedsetup()
    sched/ (plus some binfmt/, include/, and arch/):  Rename task_start() and task_starthook() to nxtask_start() and nxtask_starthook().
    arch/ and sched/:  Rename task_exit() and task_exithook() to nxtask_exit() and nxtask_exithook(), respectively.
    sched/task:  Rename all internal, static, functions to begin with the nx prefix.

sched/init/os_smpstart.c

@@ -84,7 +84,7 @@ static const char g_idlename[] = "CPUn Idle"
  *   This is the common start-up logic for the IDLE task for CPUs 1 through
  *   (CONFIG_SMP_NCPUS-1).  Having a start-up function such as this for the
  *   IDLE is not really an architectural necessity.  It is used only for
- *   symmetry with now other threads are started (see task_start() and
+ *   symmetry with now other threads are started (see nxtask_start() and
  *   pthread_start()).
  *
  * Input Parameters: