GitLab

This commit uses the `git status --porcelain -b` format to gather the
number of ahead and behind commits related to the remote branch.

This version uses `git status --porcelain` instead of making
multiple calls to `git status`.

"/usr/bin/python2" does not exist on Mac OSX (see #2382), so fuck people who have
"python" symlinked to "python3"

This reverts commit e5ed07e2

as suggested in #2382

In Python3 without universal_newlines set to True
output from Popen was byte-encoded.