Auto-generate commit message for checkintool about git-tfs

[spraints]

This shouldn't be too hard. I actually just nuked the code (the change to GetParentTfsCommits in 4e2c348) that would have made this really easy, but it should be pretty easy to add back in.

[rbanks54]

I've added this myself so that "git tfs ct" pulls the messages in for you automatically. Matt, do you want to just grab the code from my fork or do you want me to send you a pull request?

[spraints]

either one is fine.

[spraints]

rbanks54 -- I'm grabbing it from your fork. I hope to have time tomorrow to get it done.

[spraints]

Take a look at 44d6f40 ... I incorporated Richard's patch, and added a command switch. "git tfs help checkintool" will show you that you can do "git tfs checkintool --build-default-comment".

[JeremySkinner]

Brilliant - looks good.

[spraints]

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