Issue #25034: Merge from 3.5.

diff --cc Lib/string.py
Simple merge

diff --cc Misc/ACKS
Simple merge

diff --cc Misc/NEWS
index ceac0a355c79603e61873258f6ed9cced75179a7,5a7784466c2d70d2720adc73a178c9f67efee6a0..5fb3be1617f586195594828204a58e6a8ad8a7f4
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -190,8 -21,14 +190,11 @@@ Core and Builtin
  Library
  -------
  
+ - 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 #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.