bug#1863: Improved grep prompt

[Juri Linkov <juri@jurta.org>]

> JL> Everybody's using rgrep and lgrep these days
> Well I would make M-x grep say that then,

It already says that.
`C-h f grep RET':

    For doing a recursive `grep', see the `rgrep' command.
    For running `grep' in a specific directory, see `lgrep'.

> with a an option available for those who really want to use the old
> grep even after finally learning this news.

There is already a template option for the old `grep'.
`C-h v grep-command RET':

    grep-command is a variable defined in `grep.el'.
    Its value is "grep -nH -e *"

    Documentation:
    The default grep command for M-g r e.

-- 
Juri Linkov
http://www.jurta.org/emacs/