Allows profile file to work on pathmunge-less systems.

`pathmunge` is a RedHat/CentOS'ism. It isn't available on Arch Linux, for example.

This will check for `pathmunge`'s existence and use it, or fallback to
prepending to the path (when it isn't already there, which is the same behaviour as pathmunge).

My sh-fu isn't the best, so sanity-checking is appreciated.