clone: test local clone in `test-clone-uncompressed.t` too This is not an uncompressed test but needs to be tested in the same kind of constraints regarding special file name. Differential Revision: https://phab.mercurial-scm.org/D11218

test-transaction-safety: relax some of the synchronisation schedule We can have `internal` and `external` runs at the same time, so we unlock `external` a bit sooner. Differential Revision: https://phab.mercurial-scm.org/D11216

test-transaction-safety: document the test schedule This helps reader to understand how the test work and actually helped me to detect a missing synchronisation step. Differential Revision: https://phab.mercurial-scm.org/D11215