bug#16823: Use DFA regex engine on fgrep matcher

[Paul Eggert]

Thanks, I pushed your patch (with a minor change to make it integrate 
with the latest grep) and then pushed some fixes and one major 
simplification: don't have any special case for "grep -iF PAT" when PAT 
contains no alphabetics.  This is rare enough that I expect it's not 
worth complicating grep to worry about it.

I'm attaching the combined patch, that is the merge of your patch plus 
my changes.

grep-F.patch
Description: Text document