Log Message:
Add a message that a Ghostscript package is required if you want to
convert .fig files to Postscript, PDF, and the like.  This is not
a dependency, because transfig can be used without Ghostscript as
well (eg, to convert to other file formats).  Moreover, it is a
pre-requisite to Xfig, which doesn't require Ghostscript at all.

Closes PR pkg/22959 by Greg A. Woods <woods@planix.com>