Fix large update tests.

The server is less forgiving now. You can no
longer update a document to larger than 16MB.

test/test_bulk.py

@@ -584,10 +584,8 @@ class TestBulk(BulkTestBase):
         self.assertEqual(self.coll.find({'x': 2}).count(), 0)
 
     def test_upsert_large(self):
-        # We can insert a 16MB document, using an update command a little over
-        # 16MB long.
         client = self.coll.database.connection
-        big = 'a' * (client.max_bson_size - 30)
+        big = 'a' * (client.max_bson_size - 37)
         bulk = self.coll.initialize_ordered_bulk_op()
         bulk.find({'x': 1}).upsert().update({'$set': {'s': big}})
         result = bulk.execute()

test/test_collection.py

@@ -1859,7 +1859,7 @@ class TestCollection(unittest.TestCase):
         self.assertRaises(DocumentTooLarge, self.db.test.update,
                           {"bar": "x"}, {"bar": "x" * (max_size - 14)}, w=0)
         # This will pass with OP_UPDATE or the update command.
-        self.db.test.update({"bar": "x"}, {"bar": "x" * (max_size - 15)})
+        self.db.test.update({"bar": "x"}, {"bar": "x" * (max_size - 32)})
 
     def test_insert_large_batch(self):
         max_bson_size = self.client.max_bson_size