tests: add explicit coverage for update_hash_refs from rewriteutil I couldn't find any evidence this is covered by tests in core (but there's a good chance I missed it). We've seen a cute bug in that code, but first let's just cover the cases that work correctly. Differential Revision: https://phab.mercurial-scm.org/D11231

store: document the decoding discrepancy in store.py This will help future people that might be looking into this. Differential Revision: https://phab.mercurial-scm.org/D11220

clone: add a file with special character while testing uncompressed This will make sure we currently do not have any actual impact from issue6548. Differential Revision: https://phab.mercurial-scm.org/D11219