rhg: support "status FILE"...
rhg: support "status FILE"
This change adds a new [file] argument to rhg status, parses them as
patterns, canonicalizes the paths, and constructs a new PatternMatcher
to intersect with the existing matcher being passed to the status
implementation.
We also make filepatterns a public module so we can access the
pattern-parsing functionality we need from commands/status.rs.