After time.wallclock() (issue #10278), let add a time.monotomic() function. It is similar to time.wallclock() (try to get the most accurate clock) but is not available if the system doesn't provide a monotonic clock. It may also fail at runtime if Python cannot find a monotonic clock, whereas time.clock() and time.wallclock() fallback on a wallclock which may go backward on NTP adjust.

The documentation of the patch should be improved :-)

wallclock() tests may be simplified or dropped because they may fail on NTP adjust.