match: avoid accessing match._pathrestricted from subdirmatcher Accessing only the public API wherever possible helps us refactor matchers later.

match: override visitdir() the usual way in subdirmatcher Just override the function instead of replacing it on each instance.

match: make _fileroots a @propertycache and rename it to _fileset The files in the set are not necesserily roots of anything. Making it a @propertycache will help towards extracting a base class for matchers.

fsmonitor: use modern match API It seems like fsmonitor/__init__.py was based on a pretty old version of dirstate.py. Let's copy over the changes from the following two commits: 55c449345b10 (match: add isexact() method to hide internals, 2014-10-29) 3c346969c321 (dirstate: avoid match.files() in walk(), 2015-05-19)