JCR-3775: Avoid lock contention in ISO8601.parse()

We actually do need flyweight instances of other known time zones than just GMT.
Add the ones listed in http://en.wikipedia.org/wiki/List_of_UTC_time_offsets.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/trunk@1590132 13f79535-47bb-0310-9956-ffa450edef68