match: allow unioning arbitrary match functions A future patch will be allowing nested matchers. To support that, let's refactor _buildmatch to build a list of matchers then return True if any match. We were already doing that for filesets + regex patterns, but this way will be more generic.

match: add root to _buildmatch A future patch will make _buildmatch able to expand relative include patterns. Doing so will require knowing the root of the repo, so let's go ahead and pass it in.