[GRASS5] -q flag for r.cats and other commands

[John A. Preston]

> Having said that, any error message generated by G_fatal_error() will
> begin with "ERROR:", and any warning message generated by G_warning()
> will begin with "WARNING:"[1].
That's what I need for now.

> However, some programs simply print messages to stderr (or even
> stdout).
The ones to stdout I print in the log as program messages while
the ones to stderr I'll simply ignore.

Thanks.

John Preston