asyncio: Add asyncio.compat module

Move compatibility helpers for the different Python versions to a new
asyncio.compat module.
diff --git a/Lib/asyncio/locks.py b/Lib/asyncio/locks.py
index b2e516b..cc6f2bf 100644
--- a/Lib/asyncio/locks.py
+++ b/Lib/asyncio/locks.py
@@ -5,14 +5,12 @@
 import collections
 import sys
 
+from . import compat
 from . import events
 from . import futures
 from .coroutines import coroutine
 
 
-_PY35 = sys.version_info >= (3, 5)
-
-
 class _ContextManager:
     """Context manager.
 
@@ -70,7 +68,7 @@
         yield from self.acquire()
         return _ContextManager(self)
 
-    if _PY35:
+    if compat.PY35:
 
         def __await__(self):
             # To make "with await lock" work.