bug#13693: M-x grep should do some basic parameter checking

[Juri Linkov]

> JL> If you tend to forget the pattern or file argument there is a reliable 
> grep
> JL> known as `M-x rgrep' that asks you what and where to search.
>
> Yes, I use that too.
>
> And that is what is causing me to even remember less that M-x grep needs
> more arguments when I use it !

Then customize `grep-command' to something like "grep -nH -e pattern *"
that would remind you to replace the default search string "pattern"
and to replace "*" with actual file names to search.