Grep related fixes.

Grep related fixes.

* etc/grep.txt: Add `eval' to the Local Variables section that
emulates `grep-filter'.

* lisp/progmodes/grep.el (grep-filter): Avoid incomplete processing by
keeping point where processing of grep matches begins, and
continue to delete remaining escape sequences from the same point.
(grep-filter): Make leading zero optional in "0?1;31m" because
git-grep emits "\033[1;31m" escape sequences unlike expected
"\033[01;31m" as GNU Grep does.
(grep-process-setup): Replace obsolete "ml=" with newer "sl=".