Merge branch 'jc/check-x-z'

"git check-ignore -z" applied the NUL termination to both its input (with --stdin) and its output, but "git check-attr -z" ignored the option on the output side. This is potentially a backward incompatible fix. Let's see if anybody screams before deciding if we want to do anything to help existing users (there may be none). * jc/check-x-z: check-attr -z: a single -z should apply to both input and output check-ignore -z: a single -z should apply to both input and output check-attr: the name of the character is NUL, not NULL check-ignore: the name of the character is NUL, not NULL