py3: pass str in os.sysconf() os.sysconf() doesn't accepts bytes on Python 3. Adding r'' will make sure b'' is not added here.

context: move dirty() to committablectx This is a pedantic move. It should be an error if dirty() is called on a read-only context. Based on Mads Kiilerix's and my work at the sprint.

committablectx: extra is already normalized by committablectx.__init__ Avoid doing the same work again. Based on work done by Mads Kiilerix.

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.