Fix issue #4496: tslib.tz_convert(vals, tz1, tz2) may raise an IndexErro...
Bug-fix for Issue #4496 Bug: tslib.tz_convert(vals, tz1, tz2) may raise an IndexError exception.

couple of things, please do the following
- ~~add a test~~
- hook up travis CI
- add documentation to `doc/release.rst`, preferentially move the docstring in your test to release notes, but not necessary. if you just want to add a blurb that's fine too.
 - hook up travis CI // done;
- add documentation to doc/release.rst // done (not sure whether such a long bug description is appropriate in release.rst);
- "You should rewrite this according to what the hour should be here, don't catch every exception: that could hide another bug." // That's reasonable. Thanks! Fixed.
 @stenri can you rebase and hook up travis?
 Surely. I rebased  tslib_tz_convert_trans_pos_plus_1__bugfix against upstream/master (and combined all my commits into a one commit).
 @stenri can you squash into 1 commit? then will merge
 Excellent! Done.
 thanks!
