Previously, rbt patch really only worked with Git, Perforce, and

Mercurial. When running rbt patch with another SCM (say, CVS) it

would crash. This is because not all SCMs knew how to check for empty

files support. Now, all SCMs default to no empty file support and

runnign rbt patch with these SCMs no longer causes rbt to crash.

Ran unit tests.
Before applying this patch, using rbt patch in a CVS repository

would cause it to crash. After applying this patch, it no longer

crashes and the patch is applied successfully.