modules/services/printing/cupsd.nix: tell cups to use 'gstoraster' instead of 'pstoraster'

The CUPS filter has been renamed in GNU Ghostscript 9.x. Fortunately,
Ghostscript ships with a MIME conversions file that informs CUPS about this,
so linking that file into /etc/cups works fine. I'm not sure whether it's a
particularly elegant solution, though.

svn path=/nixos/trunk/; revision=31489

modules/services/printing/cupsd.nix

@@ -135,6 +135,7 @@ in
         preStart =
           ''
             mkdir -m 0755 -p /etc/cups
+            ln -f -v -s "${pkgs.ghostscript}/etc/cups/"* /etc/cups/
             mkdir -m 0755 -p ${logDir}
             mkdir -m 0700 -p /var/cache/cups
             mkdir -m 0700 -p /var/spool/cups