match: make base matcher return True for visitdir

If a matcher doesn't implement visitdir, we should be returning True so that
tree traversals are not prematurely pruned. The old value of False would prevent
tree traversals when using any matcher that didn't implement visitdir.

Differential Revision: https://phab.mercurial-scm.org/D83

mercurial/match.py

@@ -305,7 +305,7 b' class basematcher(object):'
         This function's behavior is undefined if it has returned False for
         one of the dir's parent directories.
         '''
-        return False
+        return True
 
     def always(self):
         '''Matcher will match everything and .files() will be empty --