Re: compilation mode highlighting wrong for filenames with spaces

[Richard Stallman]

    But perhaps it is here not without reason.  Some grep might use (3)
    syntax to report a line number.

I suspect that was copied from other regexps used to recognize
output from compilers.  Some compilers do or did use parens around
the line number, but I don't think any version of grep ever did so.

So I will delete those parens from the regexp in grep.el.