Handling of __next__ and next by future.utils.get_next was reversed

I assume nobody is using future.utils.get_next, because the builtin next() function exists from Python 2.6 on and meets most needs, and because nobody has noticed this before. Fixing in case it saves anyone confusion in future.

Author: GlenWalker

src/future/utils/__init__.py

@@ -527,9 +527,9 @@ def __next__(self):
         return cls
 
 if PY3:
-    get_next = lambda x: x.next
-else:
     get_next = lambda x: x.__next__
+else:
+    get_next = lambda x: x.next
 
 
 def encode_filename(filename):