phabricator: add basectx arguments to file related `phabsend` utilities This is in support of a future `--fold` option, that allows rolling up several commits into a single review with a diff from the start to the end of the range. There are no functional changes yet- the original `ctx` is also passed as the new `basectx`, which represents the first commit in the review range (similar to `qbase` in MQ parlance). Other functions will need the range of commits, but these deal with status or the diffs, so they only need the end points. Differential Revision: https://phab.mercurial-scm.org/D8306

phabricator: eliminate a couple of duplicate filectx lookups Differential Revision: https://phab.mercurial-scm.org/D8305

tests: update test-debugcommands.t stack trace checks for python3.9 Python 3.9 prints a complete filepath in more cases, so we need to handle that in our test output. Since we don't really care *that* much about the specific path formatting here, just use globbing. Differential Revision: https://phab.mercurial-scm.org/D8329

tests: update test-archive.t expectations for python3.9 changes Sigh. Differential Revision: https://phab.mercurial-scm.org/D8328

setup: relax -Werror for declaration-after-statement on Python 3.9 It turns out Python 3.9 introduces such declarations in the headers, eg cpython/abstract.h:189:5: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement] so we have to be more relaxed when compiling for 3.9. Differential Revision: https://phab.mercurial-scm.org/D8327

py3: require values in changelog extras to be bytes I don't know what happened here because b436059c1cca (py3: use pycompat.bytestr() on extra values because it can be int, 2019-02-05) came about b44a47214122 (py3: use string for "close" value in commit extras, 2018-02-11). Whatever happened, we shouldn't need to convert the values to bytes now. It's better to not convert because that might cover up bugs where someone sets a unicode value in the extras and that works until the unicode value happens to contain non-ascii (at which point it will fail because `bytestr()` expects its argument to be ascii if it's unicode). Differential Revision: https://phab.mercurial-scm.org/D8332