Expose _get_running_loop() and _set_running_loop() functions

Although they are prefixed with an underscore, these functions are
a part of asyncio API.  They will be used by third-party event loops
to enable proper behaviour of get_event_loop().

Author: 1st1

asyncio/events.py

@@ -6,6 +6,7 @@
            'get_event_loop_policy', 'set_event_loop_policy',
            'get_event_loop', 'set_event_loop', 'new_event_loop',
            'get_child_watcher', 'set_child_watcher',
+           '_set_running_loop', '_get_running_loop',
            ]
 
 import functools

tests/test_events.py

@@ -2732,16 +2732,20 @@ def get_event_loop(self):
         try:
             asyncio.set_event_loop_policy(Policy())
             loop = asyncio.new_event_loop()
+            self.assertIs(asyncio._get_running_loop(), None)
 
             async def func():
                 self.assertIs(asyncio.get_event_loop(), loop)
+                self.assertIs(asyncio._get_running_loop(), loop)
 
             loop.run_until_complete(func())
         finally:
             asyncio.set_event_loop_policy(old_policy)
             if loop is not None:
                 loop.close()
 
+        self.assertIs(asyncio._get_running_loop(), None)
+
 
 if __name__ == '__main__':
     unittest.main()