Added pickler for integrators and test.

wrappers/python/src/swig_doxygen/swig_lib/python/extend.i

@@ -454,3 +454,15 @@ Parameters:
         return self.__copy__()
   }
 }
+
+%extend OpenMM::Integrator {
+  %pythoncode {
+    def __getstate__(self):
+        serializationString = XmlSerializer.serialize(self)
+        return serializationString
+
+    def __setstate__(self, serializationString):
+        system = XmlSerializer.deserialize(serializationString)
+        self.this = system.this
+  }
+}

wrappers/python/tests/TestPickle.py

@@ -37,11 +37,11 @@ class TestPickle(unittest.TestCase):
         state = context.getState(getPositions=True, getForces=True, getEnergy=True)
 
         system2 = copy.deepcopy(system)
-        #integrator2 = copy.deepcopy(integrator)
+        integrator2 = copy.deepcopy(integrator)
         state2 = copy.deepcopy(state)
         
         str_state = pickle.dumps(state)
-        #str_integrator = pickle.dumps(integrator)
+        str_integrator = pickle.dumps(integrator)
         
         state3 = pickle.loads(str_state)
         context.setState(state3)