Git grep using emacs grep, instead of broken vc-git-grep.

Git grep using emacs grep, instead of broken vc-git-grep.

Google search first-hits this github gist wrapping of git grep with
emacs grep mode. I adjusted it a little to properly use '--no-pager'.

(vc-git-grep use of grep-find (or whatever) to dwim always does The
Wrong Thing, requiring finagling of the arguments and editing of the
command, before submitting it.)