Change default diff algorithm to patience diff

Sometimes the default diff output looks really strange. Patience diff
tends to look much better to a human. This is the default diff for bzr,
so it should be relatively safe as a default (it is only for user
display anyway).
Add modeline for filetype

Since the gitconfig file is missing the dot, filetype was not being set
automatically.
Add a set of prompt questions to commit message

These are useful for encouraging a thorough commit message that serves
as valuable documentation.

http://mislav.uniqpath.com/2014/02/hidden-documentation/