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

[jidanni]

Why doesn't M-x grep check that it has been given at least two
parameters, else it is bound to fail, as
$ grep
$ grep pattern
won't get far without some file arguments.

Yes
$ grep pattern pattern #wrong
will still pass as that would look the same as
$ grep pattern file
etc. but the check would be better than nothing.