manifest: introduce new exception to signal unavailability of fastdelta() I've spent some time reflecting on this, and I think this is the best we can do in this API contract for now. This opens the door to adding treemanifest's implementation to the list of implementers of imanifestdict. Differential Revision: https://phab.mercurial-scm.org/D8365

copies-tests: remove spurious `]` in the template Fixing this typo happily impact all the tests output. Differential Revision: https://phab.mercurial-scm.org/D8258