Implementing the -diffs flag.

[kminehart]

-diffs is supposed to only run tests on projects that have been changed in this commit.

The original plan said that "if a file was changed in this commit, then run the stage(s) for the project it is in."

However, there's an issue with that. If the test fails, and the developer goes on to modify another project, then the tests won't run for that project until it is modified again, leading to false positives.

One proposed solution would be to make the diffs based on branches.

jules test -diff origin/master

[kminehart]

HOWEVER that would not work for building on changes made on master, as the diff would always be 0. You could configure only master to run it with HEAD~1 of origin/master.