make git pre-commit hook only test files to be committed

make git pre-commit hook only test files to be committed

Right now, the git pre-commit hook is pretty annoying to work with when
development since it tests every single file.  That means notes, incomplete
stuff, etc. will be run through the tests.  So all of the files need to be
clean in order to commit even a single trivial fix.  This commit changes it
so that the pre-commit hook is only run on the files staged to be committed.