emitrevision: add a small closure to check if a base is usable We will make more use of this and make it more complex too.

chg: scale the timeout in test with the rest This should avoid some flakiness where the logs reports server shutting down.

hghave: we might need py310 and py311 at some point Some tests are already showing slightly different results on Python 3.11. The better idea would be to make them more portable, but if that's not possible, now we can use hghave detection for certain lines. I wonder if there will ever be Python 31.0 and 31.1 though.

hghave: detect Python 3.10 and 3.11 as well Noticed because test-contrib-relnotes.t was skipped.

extensions: load help from hgext.__index__ as a fallback this time Prior to 843418dc0b1b, `hgext.__index__` was consulted first if present, which caused the longer help from the extension modules to be ignored, even when available. But that change causes a bunch of test failures when the pyoxidized binary bundles *.pyc in the binary, saying the there's no help topic for `hg help $disabled_extension` and suggesting the use of `--keyword`, rather than showing a summary and indicating that it is disabled. Current failures were in test-check-help.t, test-extension.t, test-help.t, and test-qrecord.t. Ideally, we would read the various *.pyc files from memory and slurp in the docstring, but I know that they used to not be readable as resources, and I can't figure out how to make it work now. So maybe 3.9 and/or the current PyOxidizer doesn't support it yet. I got closer in py2exe with `importlib.resources.open_binary("hgext", "rebase.pyc")`, but `open_binary()` on *.pyc fails in pyoxidizer.[1] Either way, the *.pyc can't be passed to `ast.parse()` as `extensions._disabledcmdtable()` is doing, so I'm setting that aside for now. [1] https://github.com/indygreg/PyOxidizer/issues/649

extensions: process disabled external paths when `hgext` package is in-memory This fixes `hg help -e ambiguous` in test-helpt.t:2055 with the `ambiguous = !./ambiguous.py` configuration, when `hgext` is not in the filesystem (e.g. pyoxidizer builds with in-memory resources, or TortoiseHg with py2exe), but the disabled external extension is. Now instead of aborting with a suggestion to try `--keyword`, the help command prints text for the extension.