sparse: move resolving of sparse patterns for rev into core This method is reasonably well-contained and simple to move. As part of the move, some light formatting was performed. A "working copy" reference in an error message was changed to "working directory." The biggest change was to _refreshoncommit() in sparse.py. It was previously checking for the existence of an attribute on the repo instance. Since the moved function now returns empty data if sparse isn't enabled, we unconditionally call the new function. However, we do have to protect another method call in that function. This will all be unhacked eventually.