rust: add IntersectionMatcher
This will be used in the upcoming support for sparse checkouts in
Rust-augmented status and later in rhg support for sparse checkouts.
= 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 ==