Issue #10278: Drop time.monotonic() function, rename time.wallclock() to time.steady()

 * On Mac OS X, time.steady() now uses mach_absolute_time(), a monotonic clock
 * Optimistic change: bet that CLOCK_MONOTONIC and CLOCK_REALTIME are available
   when clock_gettime() is available
 * Rewrite time.steady() documentation
4 files changed