branchmap: implement __contains__() We have good occurences of `if branch in branchmap()` in our code. If __contains__() is not implemented then it will use __iter__() to find whether the element exists or not which is not good. I am bit confused that whether I should move existing callers to hasbranch() or this patch is a good way. Differential Revision: https://phab.mercurial-scm.org/D6206

--- a/mercurial/branchmap.py	Sun Mar 31 16:20:17 2019 +0300
+++ b/mercurial/branchmap.py	Sun Mar 31 16:27:10 2019 +0300
@@ -182,6 +182,9 @@
     def __getitem__(self, key):
         return self._entries[key]
 
+    def __contains__(self, key):
+        return key in self._entries
+
     def iteritems(self):
         return self._entries.iteritems()