Tomasz Kamiński 58a4a9518a Mismatch in return type of converting function is now hard error.
Change the implementation, in the way that mismatch in return
type of the from/to_sys/utc functions (not returning time_point,
or returning time_point with inappropriate clock) leads to
hard error.

Added appropariate fail test for to_sys function, including:
* returning an int
* returning time_point of wrong clock
* reutrning reference to time_point
2017-11-24 22:23:50 +01:00
..
2016-05-30 22:21:08 -04:00
2016-05-30 22:21:08 -04:00
2017-09-25 19:28:04 -04:00