Bug#618494: mention that gs opens a window

[jidanni@jidanni.org]

Package: ghostscript
Version: 9.01~dfsg-2

I discovered by accidental typing mistake an undocumented switch
$ gs -l
It opens an X-window.
Evidently this is a major part of the software.
However no being on the gs man page,
and not being in gs --help,
means it is totally wasted,
no matter what it is intended to do.

Wait. I now see
$ gs
does the same thing.
Well it is all the fault of the man page for not saying how the
software is intended to be used.

Compare the xpdf man page.