This commit introduces `rev-parse HEAD` in order to parse the commits at
which HEAD points before and after `git pull`. If the commits are the
same, the bundle is considered 'up-to-date'. If the commits are different,
then the HEAD was fast-forwarded and the bundle is considered 'updated'.

This approach is more reliable than parsing the output of the `git` command
as it can differ between OSes and locales.

Tested on Ubuntu 11.10. The control characters at the end of the output of
`git rev-parse` are stripped away using '[:cntrl:]', assuming cross-platform.