[Bug 827650] test mythmon's first commit independent of the pair of 'em

Mythmon wanted to test the first commit alone in addition to the second, but wanted a complicated solution instead of `git checkout -b some-other-branch`, rebase the top commit off, and open a new pull request just so leeroy can test.

If this is going to be a common occurrence there is a config flag to test every commit that can be changed on a per project basis. Let me know if you want it changed.