Also rewrote the guts of asyncio.Semaphore (patch by manipopopo). (Merge 3.4->3.5.)

diff --cc Misc/NEWS
index 5a7784466c2d70d2720adc73a178c9f67efee6a0,48f5c4e436ce1b8b784d6ab762855cf65f883863..a2c4020046353da13f672dbaf91ef859436cd56f
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -24,11 -81,9 +24,12 @@@ 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.