py3: define __next__ in patch.py

This needed to appease Python 3's iterator protocol.

This is crasher  #5 in Python 3.

Differential Revision: https://phab.mercurial-scm.org/D1480

mercurial/patch.py

@@ -149,6 +149,8 b' def split(stream):'
                 raise StopIteration
             return l
 
+        __next__ = next
+
     inheader = False
     cur = []