[Gm2] duplicate error messages

[SiTex Graphics]

Hi Gaius,

Working on the same DlgShell.mod module I sent earlier, I'm seeing a
bunch of duplicate error messages with the latest CVS (downloaded
today), 3 to 11 copies of each error message. I'm not sure if this a
change in the behavior of gm2 or something specific to this module.
Perhaps the error printing routine could have a simple filter that
just compares the message about to be printed to the last one emitted.

Thanks,
Scott