Add a pre-receive hook for running checkStyle on changed java files.
Add a pre-receive hook for running checkStyle on changed java files.

The hook considers changes to files over the whole range of changes
pushed (for each branch).  This means, it's possible for the user to
fix a file that fails checkstyle in a subsequent commit.

FluxAugur/git-hooks,FluxAugur/git-hooks,paulcadman/git-hooks