bug#7952: 24.0.50; crash in find_interval

[Chong Yidong]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

> As can be seen by a comment in grep.el, I consider grep's updating of
> the buffer as a problem.  Also, we've seen other reasons why grep's
> handling of escape sequences should be performed in the process filter
> rather than in font-lock.  So I'd rather say that grep's use of
> font-lock is wrong, rather than change jit-lock to accommodate it.

I've committed a fix for grep.el.