log: fix log -f slow path to actually follow history The revset created when -f was used with a slow path (for patterns and directories) did not actually contain any logic to enforce follow. Instead it was depending on the passed in subset to already be limited (which was limited to :. but not ::.). This fixes it by adding a '& ::.' to any -f log revset. hg log -f <file> is still broken, in that it can return results that aren't actually ancestors of the current file, but fixing that has major perf implications, so we'll deal with it later.