revlog: add __contains__ for fast membership test

Because revlog implements __iter__, "rev in revlog" works but does silly O(n)
lookup unexpectedly. So it seems good to add fast version of __contains__.

This allows "rev in repo.changelog" in the next patch.

mercurial/changelog.py

@@ -143,6 +143,11 b' class changelog(revlog.revlog):'
             if i not in self.filteredrevs:
                 return self.node(i)
 
+    def __contains__(self, rev):
+        """filtered version of revlog.__contains__"""
+        return (revlog.revlog.__contains__(self, rev)
+                and rev not in self.filteredrevs)
+
     def __iter__(self):
         """filtered version of revlog.__iter__"""
         if len(self.filteredrevs) == 0:

mercurial/revlog.py

@@ -277,6 +277,8 b' class revlog(object):'
 
     def tip(self):
         return self.node(len(self.index) - 2)
+    def __contains__(self, rev):
+        return 0 <= rev < len(self)
     def __len__(self):
         return len(self.index) - 1
     def __iter__(self):