The `git status --porcelain` command can take an additional argument
`-b` which causes the porcelain output to also contain branch
information in a stable and supposedly nonchanging way.
This change adds that argument to the initial `git status` call, and
parses the branch/ahead/behind information from that. The end result is
the entire call to `git branch -v` can be removed, resulting in one less
subshell command and hopefully a more reliable target across future
versions of git.
23e99709da