merge: remove direct rustmod reference We shouldn't rely on this member being present in `dirstate.py`, this creates unnecessary coupling. This also can trigger certain issues in edge-cases where the policy is changed at runtime or multiple Python environments fight, which is an added bonus. Differential Revision: https://phab.mercurial-scm.org/D12217

= Mercurial XXX =

== New Features ==

== Default Format Change ==

These changes affect newly created repositories (or new clones) done with
Mercurial XXX.

== New Experimental Features ==

== Bug Fixes ==

== Backwards Compatibility Changes ==

== Internal API Changes ==

== Miscellaneous ==