grep 2.5.1: NUL byte doesn't match a complemented character class

[Joe Wells]

In grep 2.5.1, a NUL character doesn't match a complemented character
class.

To reproduce:

1. Run the command “grep '[^x]x'”

2. Type the line consisting of the NUL character (the single byte with
   all bits off) followed by “x”.  How to do this depends on your tty
   settings and your terminal.  In my gnome-terminal I can do this by
   typing these keys: Control-V Control-2 x Return.  (Yes, I really
   mean Control-2.)

3. Observe that grep doesn't output anything, despite the fact that
   NUL is distinct from “x” and hence should match “[^x]”.  (A
   separate test reveals that NUL does match the pattern “.”, so
   clearly grep is seeing the character and can pass it through if it
   thinks it matches the pattern.)

Hopefully this bug has been fixed since version 2.5.1 was released,
but just in case I report it.

-- 
Joe