All tools that implement handle_file() were calling

get_patched_file_path() on the reviewed file, and returning early if

it was None. Rather than do this in each handle_file() method, it

makes more sense to do it in handle_files(), before calling

handle_file().
This change switches to that, and passes in the resulting path as a

path variable, so handle_file() can operate on it.
We don't perform the check or pass in path for legacy tools, since the

old handle_file() didn't accept **kwargs and wouldn't expect it.
To handle the legacy tool check, the old base classes now set a

legacy_tool attribute, which the inner class can check. This is

admittedly pretty hacky, but won't exist past Review Bot 3.0, and is

easier to maintain than forking these methods into the old base classes.

Unit tests pass on Python 2.7 and 3.x.