tags: change format of tags cache files .hgtags fnodes are now written to a shared cache file. They don't need to exist in the per-filter tags cache files. Stop writing them. The format of the tags cache file has changed in a backwards incompatible way. This should be acceptable, as we just established per-filter tags cache files and no client should have per-filter tags cache files that will need to be read. So no backwards compatbility concern is present. The new format has a single header line followed by resolved tags entries. The header line is similar to the old first line with a major difference: we now compute and store a hash of the filtered revisions. Before, if the set of filtered revs changed, we may return incorrect results. We now detect that. A test for verifying filtered rev change is handled properly has been added.