Make sure that branches looking like a numeric scalar will not become number type in python.

The latter will break code that assumes it will get a string.

Author: Byron

git/objects/submodule/base.py

@@ -895,7 +895,7 @@ def iter_items(cls, repo, parent_commit='HEAD'):
             u = parser.get_value(sms, 'url')
             b = cls.k_head_default
             if parser.has_option(sms, cls.k_head_option):
-                b = parser.get_value(sms, cls.k_head_option)
+                b = str(parser.get_value(sms, cls.k_head_option))
             # END handle optional information
 
             # get the binsha