Make ecore_time_get and friends use monotonic clock

Make ecore_time_get and friends use monotonic clock
Instead of relying on unix time, use a monotonic clock provided by
clock_gettime(). If a monotonic clock is not available, it will fallback
to CLOCK_REALTIME or unix time if neither is available.

The impact is that now it only makes sense to call ecore_time_get() or
ecore_time_loop_get() if the value retrieved is intended to be used as
relative to previous/posterior measurements. If an absolute value is
needed, the right function to call now is ecore_time_unix_get() which
will give the number of seconds since Jan 1st, 1970, 12:00AM.

git-svn-id: svn+ssh://svn.enlightenment.org/var/svn/e/trunk/ecore@52824 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33