Re-evaluate FAKETIME environment when cache expires

When the cache expires, the FAKETIME environment does not get re-evaluated
if FAKETIME value changes. This used to work on libfaketime-0.9.1, but was
broken at some point afterwards. This fixes this problem

Signed-off-by: Jon Ringle <jringle@gridpoint.com>
Don't parse user_faked_time if it hasn't changed

Signed-off-by: Jon Ringle <jringle@gridpoint.com>
Reset ftpl_starttime when setting new relative FT_START_AT time

Signed-off-by: Jon Ringle <jringle@gridpoint.com>
Merge pull request #55 from ringlej/feature/fix-FAKETIME-cache

Feature/fix faketime cache