Issue #25034: Merge from 3.4.

diff --cc Lib/string.py
Simple merge

diff --cc Lib/test/test_string.py
Simple merge

diff --cc Misc/ACKS
Simple merge

diff --cc Misc/NEWS
index d352296beb0907e96573b8f9b7dae1b0400cc3d0,0a2411da432f3ea92c3a7853825847ee27e51a40..5a7784466c2d70d2720adc73a178c9f67efee6a0
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -21,11 -78,11 +21,14 @@@ 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.