Garbage collect libgnomeprint

- Stage support for all -reference ports
- Nuke NOPORTDOCS, those ports are already IGNOREd with NOPORTDOCS

Approved by:	kwm (maintainer)

Add NO_STAGE all over the place in preparation for the staging support (cat:
print)

- Add header in these *-reference ports.
- Fix a few of pkg-descr by chase the rename.
- Move all PORTREVISION and PORTEPOCH to top with ?=.
- Put USE_X_PREFIX back in, but under REFERENCE_PORT, and remove PREFIX? and
  USE_XLIB. This fix ports to use the correct mtree when you change the prefix,
  for example:

        Incorrect: (Without USE_X_PREFIX)
        ================================
        # cd /usr/ports/x11-toolkits/gtk20
        # make -V MTREE_FILE
        /etc/mtree/BSD.x11-4.dist
        # make PREFIX=/tmp/foo -V MTREE_FILE
        /etc/mtree/BSD.local.dist <-- Here...
        ================================

- Add pkg-descr

Requested by:   Dan Langille <dan@langille.org> for freshports.org

Move the libgnomeprint programming reference to the
libgnomeprint-reference port.