Paul Eggert wrote:
> I'll look into writing patches for that, one for grep (which affects
> dfa.c), one for gawk (which will use the same patches to dfa.c).

OK, I got it to work, and it simplifies grep (not surprising) and gawk 
as well (a bit surprising, but there it is).  I'm attaching the patches, 
one for each program.  These patches include Paolo's original suggestion 
at the start of bug#17157, plus several other simplifications to dfa.c.