"grep '\]'" warnings suggest a Gnulib DFA patch

[Paul Eggert]

While testing, I discovered that master-branch grep's bootstrap script 
contained a regular expression with '\]' that master-branch grep now 
warns about. I fixed this portability bug in 'bootstrap' by installing 
the following patch into Gnulib and propagating this into grep master:

https://git.savannah.gnu.org/cgit/gnulib.git/commit/?id=762bd0aa660b0c1c02597e0d2e5c5fbf9bab1b91

Even though POSIX says the interpretation of \] is undefined (which 
means the Gnulib patch is helpful), it's unlikely that any 
POSIX-conforming regular expression matcher would do anything other than 
treat \] like plain ]. And this suggests that GNU grep's warning about 
\] is perhaps more trouble than it's worth.

So, what do you think of the idea of not warning for this particular 
stray backslash? Proposed Gnulib patch attached, with the idea of 
propagating this into GNU grep before its upcoming release. I haven't 
installed this.

0001-dfa-do-not-warn-about.patch
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