Include git repository information in the script execution summary

[jmgate]

For scripts that are run from within a git repository, it'd be real nice to include some git details. E.g.,

Detail	So users realize
Repository path	They're using this local clone vs that one
Remotes configured	They've cloned from this remote vs that one
Commit checked out	Which version of the script was executed
Branch/tag information	Which branch they're on, as they probably won't recognize a SHA1
Any changes in the index	What they're running locally may differ from someone else using the same commit

If the script isn't being run from within a repository, then this extra section should just be omitted.