Update to RavenDB 2.5.2700
Prohibit local or unspecified effective dates.

Local and Unspecified DateTimes do not uniquely represent a moment in
time.  This change was required because if a DateTime was passed before,
it would be implicitly converted to a DateTimeOffset and allowed.
Fix broken unit tests

Test with UTC DateTimes, since we do not allow Unspecified or Local
anymore.
Version Bump 2.5.3