test: use `wait-on-file` in `test-racy-mutations.t` The official utility scale its timeout with the run-tests.py one. So lets use it. Differential Revision: https://phab.mercurial-scm.org/D12382

amend: fix amend with copies in extras If copy information is stored only in the commit extras and not in filelogs, then they get lost on amend if the file wasn't also modified in the working copy. That's because we create `filectx` object from the old commit in those cases, and the `.copysource()` of such objects read only from the filelog. This patch fixes it by always creating a new `memfilectx` in these cases, passing the calculated copy information to it. Differential Revision: https://phab.mercurial-scm.org/D12387

tests: demonstrate that copy info in changeset gets lost on amend When copy information is stored in changesets, it gets lost on amend. We didn't notice that until now because our users at Google have the config set to `compatibility`, which means copy information is stored in both changeset and filelogs. Differential Revision: https://phab.mercurial-scm.org/D12386