contrib: import the relnotes script from the release-tools repo I figure this makes more sense to keep in the main repo, as it's a guide of sorts on how to use the releasenotes extension in the presence of commits that don't get relnotes annotations. Ported to Python 3, cleaned up some logic in a few places, but for the most part it's what we've been using for years. Differential Revision: https://phab.mercurial-scm.org/D4291

hghave: move from requiring the PYTHON3 env var to looking for `python3` We're starting to write new utility scripts in Python 3, and I think it's reasonable to expect `python3` to be something we should use if it's present. I wrote the regex to specifically ban Python 3 prior to Python 3.5 because we won't ever support that. I moved the only test that was using $PYTHON3 to just using `python3` directly. Differential Revision: https://phab.mercurial-scm.org/D4290

rename: return error status if any rename/copy failed Ever since 447ea621e50e (copy: propagate errors properly, 2007-12-06), we have returned an error status if the source file did not exist. That commit did not return error status for any other errors, and it's unclear if that was on purpose or not. It seems to me like we should return an error in the other cases to, so that's what this patch does. Differential Revision: https://phab.mercurial-scm.org/D4419

rename: emit hint about using --after consistently Both the code and the message for the case where the source file was missing was inconsistent with the other similar messages. Differential Revision: https://phab.mercurial-scm.org/D4418

rename: quote hg commands in warnings I think we usally use single quotes around hg commands in messages. Differential Revision: https://phab.mercurial-scm.org/D4417

zsh_completion: complete hg files Differential Revision: https://phab.mercurial-scm.org/D4361

zsh_completion: adjust usage of common options addremove, remove and serve accept -S/--subrepos, and purge actually doesn't. qnew accepts -I/--include and -X/--exclude. qrefresh accepts -D/--currentdate, -U/--currentuser, -d/--date and -u/--user. rebase accepts -n/--dry-run. Differential Revision: https://phab.mercurial-scm.org/D4360

resolve: make condition clearer, and able to handle a new flag Differential Revision: https://phab.mercurial-scm.org/D4377

shelve: drop mention of obsshelve file Core shelve extension does not use obsolescence, we clean up this unused file before adding a new info file.

shelve: rename method for data write/read There are no user of this code nor any code related to obsshelve in the extensions right now, so we rename the function before using them. Note: The shelvedfile looks a bit strange. We should probably refactor it, however, this is an adventure for another series.