manifest-cache: ignore IOError while writing If the wcache directory is non writable for some reason (eg: belong to root). Trying to write to it currently crash Mercurial. Instead we ignore the error and skip writing that cache. We should probably improve the user experience of multiple users interacting with the same repository. However this is not an adventure for stable. Differential Revision: https://phab.mercurial-scm.org/D8512

copy: give better error message when no source paths found with --at-rev The new error message matches what we show when marking copies in the working copy. Differential Revision: https://phab.mercurial-scm.org/D8496

tests: show poor error message for `hg cp -A --at-rev . non-existent dst` Differential Revision: https://phab.mercurial-scm.org/D8495