match: introduce explicitdir and traversedir

match.dir is currently called in two different places:
(1) noting when a directory specified explicitly is visited.
(2) noting when a directory is visited during a recursive walk.

purge cares about both, but commit only cares about the first.

Upcoming patches will split the two cases into two different callbacks. Why
bother? Consider a hypothetical extension that can provide more efficient walk
results, via e.g. watching the filesystem. That extension will need to
fall back to a full recursive walk if a callback is set for (2), but not if a
callback is only set for (1).

mercurial/match.py

@@ -121,6 +121,10 b' class match(object):'
         pass
     def dir(self, f):
         pass
+    def explicitdir(self, f):
+        self.dir(f)
+    def traversedir(self, f):
+        self.dir(f)
     def missing(self, f):
         pass
     def exact(self, f):