ENH: Add repository revision support

[westurner]

For the sh report, (optionally?) include the requisite vcs commands to replicate the HEAD of each repository working directory:

• cd $dir
• git checkout [...] [--track <remote/branch>] and/or git pull
• hg checkout [-c]
• svn
• bzr

git remote
git remote help
git remote add upstream ssh://git@github.com/westurner/pyrpo
git remote remove upstream
git remote set-url upstream ssh://git@github.com/westurner/pyrpo

hg r