Augment Python Path with all "pylib" directories in Vim runtimepath.
Move sniputil.py to common pylib directory for easier sharing.

Add "setpypath.py" files into UltiSnips directories to avoid
duplicating sys.path logic for locating sniputil.py; update all
UltiSnips/*.snippets.py files to use setpypath.
Merge uses of betterVisual from John Szakmeister's pull request.

Request URL:  https://github.com/drmikehenry/vimfiles/pull/122
Record changes for Python sys.path augmentation.
user/jszakmeister: create some specialized mappings for ``git rebase``
user/jszakmeister: highlight diffs in emails
user/jszakmeister: treat certain patch files as email

This is useful when editing patch files generated by `git format-patch`
or `git send-email --annotate` when sending patches to a list.  You
often include information below the --- marker in response to feedback
on the list.
user/jszakmeister: teach gV to match the original visual selection mode