towards gridfs 1.0: support metadata

gridfs/grid_file.py

@@ -151,6 +151,7 @@ class GridFile(object):
     chunk_size = __create_property("chunkSize", True)
     upload_date = __create_property("uploadDate", True)
     aliases = __create_property("aliases")
+    metadata = __create_property("metadata")
     next = __create_property("next", True)
 
     def rename(self, filename):

test/test_grid_file.py

@@ -150,6 +150,7 @@ class TestGridFile(unittest.TestCase):
         self.assertEqual(a.chunk_size, 256000)
         self.assertTrue(isinstance(a.upload_date, datetime.datetime))
         self.assertEqual(a.aliases, None)
+        self.assertEqual(a.metadata, None)
         self.assertEqual(a.next, None)
 
         a.content_type = "something"
@@ -170,6 +171,9 @@ class TestGridFile(unittest.TestCase):
         a.aliases = ["hello", "world"]
         self.assertEqual(a.aliases, ["hello", "world"])
 
+        a.metadata = {"something": "else"}
+        self.assertEqual(a.metadata, {"something": "else"})
+
         def set_next():
             a.next = None
         self.assertRaises(AttributeError, set_next)