Subversion's patching functionality has been moved to the new Patcher API,

giving us a more future-proof, standardized way of patching and reverting,

handling empty files and conflicts.
There's a lot to Subversion patching. They use their own proprietary

patch format and output, and need special logic for adding or deleting

empty files. The old logic for all this has been moved into

SVNPatcher.
This did require some fixes to the base patching support to default

patch prefix levels to None instead of 0, and to

BaseSCMClient.apply_patch() to pass in the repository info to the

patcher.

All unit tests pass.