lfs: add a fileset for detecting lfs files This currently has the same limitation as {lfs_files}, namely it doesn't report removed files. We may want a dedicated 'lfs()' revset for efficiency, but combining this with the 'contains()' revset should be equivalent for now. Combining with 'set:added()' or 'set:modified()' inside 'files()' should be equivalent to a hypothetical lfs_adds() and lfs_modifies(). I wonder if there's a way to tweak the filesets to evaluate lazily, to close the efficiency gap. It would also be interesting to come up with a template filter for '{files}' that looked at the pattern to 'files()', and filtered appropriately. While passing a fileset as the pattern to `hg log` does filter '{files}', the set is evaluated against the working directory, so there's no way to list all non-lfs files above a certain size in all revisions, for example.