Also rewrote the guts of asyncio.Semaphore (patch by manipopopo). (Merge 3.5->3.6.)

diff --cc Misc/NEWS
index 5fb3be1617f586195594828204a58e6a8ad8a7f4,a2c4020046353da13f672dbaf91ef859436cd56f..861b83e22e40e762e1b312f35e9cfd419ce1f5fa
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -193,8 -24,12 +193,9 @@@ Librar
  - Issue #25034: Fix string.Formatter problem with auto-numbering and
    nested format_specs. Patch by Anthon van der Neut.
  
- - Issue #25233: Rewrite the guts of asyncio.Queue to be more understandable and correct.
+ - Issue #25233: Rewrite the guts of asyncio.Queue and
+   asyncio.Semaphore to be more understandable and correct.
  
 -- Issue #25203: Failed readline.set_completer_delims() no longer left the
 -  module in inconsistent state.
 -
  - Issue #23600: Default implementation of tzinfo.fromutc() was returning
    wrong results in some cases.