[libgnomeprint] missing dependency on libgnomecups

[Martijn Brouwer <e a m brouwer tnw utwente nl>]

Hi Paul and others,
Paul: thanks for making available a tarball so soon after the release of
2.8.1.
I encountered this error: libgnomeprint depends on libgnomecups, but
this dependency is not listed in the Makefile. Obviously this has to be
added. Secondly, since libgnomeprint depends on libgnomecups, the later
should be moved from geektoys to platform.

Martijn Brouwer