Sync with CPython (PEP 492 __aiter__ update)

Author: 1st1

asyncio/compat.py

@@ -4,6 +4,7 @@
 
 PY34 = sys.version_info >= (3, 4)
 PY35 = sys.version_info >= (3, 5)
+PY352 = sys.version_info >= (3, 5, 2)
 
 
 def flatten_list_bytes(list_of_data):

asyncio/streams.py

@@ -689,3 +689,9 @@ def __anext__(self):
             if val == b'':
                 raise StopAsyncIteration
             return val
+
+    if compat.PY352:
+        # In Python 3.5.2 and greater, __aiter__ should return
+        # the asynchronous iterator directly.
+        def __aiter__(self):
+            return self