match: don't remove '.' from _includeroots

This makes _includeroots more like _fileroots and gives visitdir() a
nice symmetry in the two.

I'm hoping to later combine the two (_fileroots and _includeroots),
and having them treated similarly should make that step easier to
follow.

mercurial/match.py

@@ -126,7 +126,6 b' class match(object):'
             self.includepat, im = _buildmatch(ctx, kindpats, '(?:/|$)',
                                               listsubrepos, root)
             self._includeroots.update(_roots(kindpats))
-            self._includeroots.discard('.')
             self._includedirs.update(util.dirs(self._includeroots))
             matchfns.append(im)
         if exclude:
@@ -225,6 +224,7 b' class match(object):'
         if dir in self._excluderoots:
             return False
         if (self._includeroots and
+            '.' not in self._includeroots and
             dir not in self._includeroots and
             dir not in self._includedirs and
             not any(parent in self._includeroots