[lib] Bug #134: threads should be more robust against backward time jumps

[lib] Bug #134: threads should be more robust against backward time jumps

2006-08-25 Paul Jakma <paul.jakma@sun.com>

	* thread.c: (general) Add support for monotonic clock, it may still
	  jump forward by huge amounts, but should be immune to going
	  backwards. Fixes bug #134.
	  (quagga_gettimeofday_relative_adjust) helper, does what name
	  says - adjusts gettimeofday based relative timer.
	  (quagga_gettimeofday) helper to keep recent_time up to date.
	  (quagga_get_relative) helper, update and getch the relative
	  timer using gettimeofday(). POSIX CLOCK_MONOTONIC is also
	  supported, but the code is not enabled yet nor tested.
	  (quagga_real_stabilised) helper, retrieve absolute time but
	  stabilised so as to never decrease.
	  (quagga_gettime) Exported interface, analogous to POSIX
	  clock_gettime() in interface, supporting several clocks.
	  (quagga_time) Exported interface, analogous to traditional
	  time(), will never decrease.
	  (recent_relative_time) Convenience function to retrieve
	  relative_time timeval, similar to existing recent_time absolute
	  timeval, for when an approximately recent value will do.
	  (remainder) Update to use above helpers.
	  (thread_getrusage) Previously was a macro, but needs to be
	  a function to twiddle with thread.c private stuff.
	* thread.c: Point the GETRUSAGE macro at previous function.
	  Export quagga_gettime, quagga_time and recent_relative_time for
	  general use.