Optimize 'OFS.ObjectManager.__contains__' method

Backported from master.

doc/CHANGES.rst

@@ -8,7 +8,9 @@ http://docs.zope.org/zope2/
 2.13.25 (unreleased)
 --------------------
 
-- TBD
+- Optimized the `OFS.ObjectManager.__contains__` method to do the
+  least amount of work necessary.
+
 
 2.13.24 (2016-02-29)
 --------------------

src/OFS/ObjectManager.py

@@ -787,7 +787,11 @@ class ObjectManager(CopyContainer,
         return self._setObject(key, value)
 
     def __contains__(self, name):
-        return name in self.objectIds()
+        for ob in self._objects:
+            if name == ob['id']:
+                return True
+
+        return False
 
     def __iter__(self):
         return iter(self.objectIds())