match: introduce nevermatcher for when no ignore files are present 952017471f93 introduced a deterministic `__repr__` for ignores. However, it didn't account for when ignore was `util.never`. This broke fsmonitor's ignore change detection -- with an empty hgignore, it would kick in all the time. Introduce `nevermatcher` and switch to it. This neatly parallels `alwaysmatcher`.

check-code: suggest policy.importmod This forbids patterns like `from mercurial.cext import parsers` which breaks pure.

test-obsolete-bundle-strip: test bundling in the seventh case Updating all cases in the file at the same time is a bit overwhelming and harder to double check. So each case come in its own patch.

test-obsolete-bundle-strip: test bundling in the sixth case Updating all cases in the file at the same time is a bit overwhelming and harder to double check. So each case come in its own patch.

test-obsolete-bundle-strip: test bundling in the fifth case Updating all cases in the file at the same time is a bit overwhelming and harder to double check. So each case come in its own patch.

test-obsolete-bundle-strip: test bundling in the fourth case Updating all cases in the file at the same time is a bit overwhelming and harder to double check. So each case come in its own patch.

test-obsolete-bundle-strip: test bundling in the third case Updating all cases in the file at the same time is a bit overwhelming and harder to double check. So each case come in its own patch.

test-obsolete-bundle-strip: test bundling in the second case Updating all cases in the file at the same time is a bit overwhelming and harder to double check. So each case come in its own patch.

test-obsolete-bundle-strip: test bundling in the first case We adds a shell function checking that the relevant markers and the bundled markers matches. Updating all cases in the file at the same time is a bit overwhelming and harder to double checks. So each cases come in its own patch.

obsolete: raise richer exception on unknown version We raise a more precise subclass of Abort with details about the faulty version. This will be used to detect this case and display some information in debugbundle.