rename: add support for --at-rev, which marks as copy and removes the source I had previously only added support for `--at-rev` to `hg cp`, but not to `hg mv`. This patch adds that support. Just like for `hg cp`, it marks the destination as copied from the source, and doesn't care if the source file still exists (because it only supports the `-A` mode, aka "don't touch files" mode). It works whether or not the source file still exists. This matches the behavior of `hg mv -A` in the working copy. Differential Revision: https://phab.mercurial-scm.org/D8840

tests: make test-install.t work on debian systems Debian systems, at least as of their version of python3.8 on my machine, have rewritten some logic in ensurepip to make it not use the wheels in pip._bundled, but instead to use wheels installed in /usr/share/python-wheels. It copies these wheels into the virtual environment when it's created, and installenv/bin/pip is able to see them and use them, so it thinks that 'wheel' is installed, and that it can build the mercurial wheel instead of just installing it. For some reason, when it subprocesses to run `python3 setup.py bdist_wheel`, it setup.py does *not* have the 'wheel' wheel available, and we get an error message. Differential Revision: https://phab.mercurial-scm.org/D8813

rhg: handle broken pipe error for stderr Differential Revision: https://phab.mercurial-scm.org/D8871

rhg: extract function handle_stdout_error Avoid repeating the logic of handling stdout write errors. Differential Revision: https://phab.mercurial-scm.org/D8870

rhg: add a limited `rhg files` subcommand Differential Revision: https://phab.mercurial-scm.org/D8869

rhg: add a `Files` `Command` to prepare the `rhg files` subcommand Differential Revision: https://phab.mercurial-scm.org/D8868

rhg: simplify `FindRootError` handling Differential Revision: https://phab.mercurial-scm.org/D8867

rhg: add buffered stdout writing possibility Improve batch stdout writing performance. At some point line buffered output should be introduced. Differential Revision: https://phab.mercurial-scm.org/D8866

rhg: ask the error message from `CommandError` Avoid repeating the display of the same error messages in different commands. Differential Revision: https://phab.mercurial-scm.org/D8865

rhg: Do not return error when when we really mean ok in commands Before when a command was successfull `Err(CommandErrorKind::Ok.into())` was returned which is an oxymoron. Using `Ok(())` when everything is ok seems more appropriate. Differential Revision: https://phab.mercurial-scm.org/D8864