spanset: use base implementation for __add__

spanset: use base implementation for __add__

--- a/mercurial/revset.py	Fri Oct 03 00:31:18 2014 -0500
+++ b/mercurial/revset.py	Fri Oct 03 00:31:33 2014 -0500
@@ -2919,14 +2919,6 @@
             return True
         return False
 
-    def __add__(self, x):
-        kwargs = {}
-        if self.isascending() and x.isascending():
-            kwargs['ascending'] = True
-        if self.isdescending() and x.isdescending():
-            kwargs['ascending'] = False
-        return _addset(self, x, **kwargs)
-
     def __len__(self):
         if not self._hiddenrevs:
             return abs(self._end - self._start)