ChangeLog

	  safe since the new features are only enabled by this option (Safer
	  but not 100% safe since it does not protect from typos and other
	  dumb errors) (2014-8-6).
	* arch/sim/src/Makefile, up_idle.c, up_internal.h, and up_tickless.c:
	  Add support for a simulated interval timer support verification of
	  the tickless OS (2014-8-6).
	* include/nuttx/arch.h: Added another tickless OS interface to get
	  the timer remaining on the interval timer (2014-8-6).
	* include/nuttx/clock.h, sched/clock_initialize.c and clock_internal.h:
	  If CONFIG_SCHED_TICKLESS is defined, then the global variable
	  g_system_timer does not exist (2014-8-6).
	* sched/Makefile: Don't build in sched_processtimer.c if
	  CONFIG_SCHED_TICKLESS is selected (2014-8-6).
	* sched/clock_gettime.c and clock_settime.c: Use the clock_systimer()
	  macro, do access the g_system_timer() global directly (2014-8-6).
	* sched/clock_systimer.c: Uses interval timer interfaces to get the
	  time if CONFIG_SCHED_TICKLESS is selected (2014-8-6).
	* sched/sched_timerexpiration.c, Makefile, os_internal.h,
	  sched_addreadytorun.c, sched_processtimer.c, sched_unlock.c,
	  wd_cancel.c, wd_internal.h, and wd_start.c: Implements the
	  tickless OS (2014-8-7).
	* Many files: Remove CONFIG_DISABLE_CLOCK.  Why?  This option is not
	  really very useful and was only selected in a few unusable, mostly
	  unusable configurations anyway (m9s12/ostest, kl25z/minnsh,
	  z180/ostest, 8051, sh1, z80, and z8).  The only real loss is probably
	  to the kl25z/minsh configuration .  And with the addition of the
	  tickless OS, I just wanted to make the pain go away (2014-8-7).
	* Many files: Change CONFIG_MSEC_PER_TICK to CONFIG_USEC_PER_TICK.
	  This gives more options for system timers in general, but more
	  importantly, let's us realize higher resolution for the case of
	  CONFIG_SCHED_TICKLESS=y -- of course, at the risk of some new
	  integer overflow problems 2014-8-7).
	* Many files: Change all time conversions.  Yech.  New timer units
	  in microseconds breaks all existing logic that used milliseconds
	  in the conversions.  Something likely got broken doing this,
	  probably because I confused a MSEC2TICK conversion with a TICK2MSEC
	  conversion (2014-8-7).
	* arch/sim/src/up_tickless.c and sched/sched_timerexpiration.c: The
	  tickless OS now appears fully functional and passes the OS test
	  on the simulator with no errors (2014-8-7).
	* sched/mqueue: Move POSIX message queue files from sched/ to
	  sched/mqueue (2014-8-8).
	* sched/signal: Move signal-related files from sched/ to sched/signal
	  (2014-8-8).
	* sched/pthread: Move all pthread files from sched/ to sched/pthread
	  (2014-8-8).
	* sched/semaphore: Move POSIX counting semaphore files from sched/ to
	  sched/semaphore (2014-8-8).
	* sched/environ: Move environment files from sched/ to sched/environ
	  (2014-8-8).
	* sched/group: Move group logic from sched/ to sched/group (2014-8-8).
	* sched/wdog: Move watchdog functions from sched/ to sched/wdog
	  (2014-8-8).
	* sched/irq: Move interrupt dispatch logic from sched/ to sched/irq
	  (2014-8-8).
	* sched/clock: Move clock functions from sched/ to sched/clock
	  (2014-8-8).
	* sched/timer: Move POSIX timer files from sched/ to sched/timer
	  (2014-8-8).
	* sched/paging: Move page fill sources from sched/ to sched/paging
	  (2014-8-8).
	* sched/init: Move initialization functions from sched/ to sched/init
	  (2014-8-8).
	* sched/errno: Move errno related files from sched/ to sched/errno
	  (2014-8-8).
	* sched/task: Move task control files from sched/ to sched/task
	  (2014-8-8).
	* sched/: Move a few files in sched/ that did not seem to have a home to
	  sched/signal and sched/task (2014-8-8).
	* sched/sched: Move scheduler files from sched/ to sched/sched
	  (2014-8-8).
	* (Many files): Replace os_internal.h with sched/sched.h in files that
	  actually reference something in sched.h (2014-8-8).
	* sched/task/exit.c: Move sched/exit.c to sched/task/exit.c (2014-8-8).
	* (Many files): Remove os_internal.h it has been replace by several new
	  header files under sched/.  There have been some sneak inclusion paths
	  via os_internal.h, so expect a few compilation errors for some
	  architectures (2014-8-8).
	* Documentation/NuttxPortingGuide.html, arch/sim/src/up_tickless.c, and
	  include/nuttx/arch.h: Fix errors in documentation and comments related
	  to the Tickless OS.  From Vijay Kumar (2014-9-9).