test/python: add test Model

unittest/python/CMakeLists.txt

 SET(${PROJECT_NAME}_PYTHON_TESTS
   bindings
+  bindings_model
   bindings_data
   bindings_com
   bindings_com_velocity_derivatives

unittest/python/bindings_model.py

+import unittest
+import pinocchio as pin
+pin.switchToNumpyMatrix()
+
+from test_case import TestCase
+
+class TestModel(TestCase):
+    def setUp(self):
+        self.model = pin.buildSampleModelHumanoidRandom()
+
+    def test_pickle(self):
+        import pickle
+
+        model = self.model
+        pickle.dump(model, open( "save.p", "wb" ) )
+      
+        model_copy = pickle.load( open( "save.p", "rb" ) )
+        self.assertTrue(model == model_copy)
+
+if __name__ == '__main__':
+    unittest.main()