vfs: simplify path audit disabling in stream clone
The whole 'mustaudit' API is quite complex compared to its actual usage by its
unique user in stream clone.
Instead we add a "auditpath" parameter to 'vfs.__call_'. The stream clone code
then explicitly open files with path auditing disabled.
The 'mustaudit' API will be cleaned up in the next changeset.
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).