Better message for `git infer` when there's nothing to infer

[rec]

Beta tester report:

When there are no tracked les, and we use git-infer -a, we don't get any message saying that there aren't any tracked les to commit. I feel it would be better to give a message that there aren't any les to commit.

git-infer is written by someone else and so it's in bash and thus harder to add features. I am contemplating simply porting it to Python so I could make use of all the features I have in Python.