datetime utilities:  - add support for `'iso8601'` format in format utilities and also in `parse_date`  - change names of !FixedOffset timezones, from the ''Etc/GMT-/+'' POSIX names to the more intuitive ''GMT +/-'' ones, as discussed in #975.
datetime utilities:
 - add support for `'iso8601'` format in format utilities and also in `parse_date`
 - change names of !FixedOffset timezones, from the ''Etc/GMT-/+'' POSIX names to the more intuitive ''GMT +/-'' ones, as discussed in #975.

(merged from the source:sandbox/timeline-link-resolver-tmp branch)

git-svn-id: eda3d06fcef731589ace1b284159cead3416df9b@4645 af82e41b-90c4-0310-8c96-b1721e28e2e2

walty8/trac,jun66j5/trac-ja,netjunki/trac-Pygit2,walty8/trac,jun66j5/trac-ja,jun66j5/trac-ja,walty8/trac,walty8/trac,jun66j5/trac-ja,netjunki/trac-Pygit2,netjunki/trac-Pygit2