Upgrade port graphics/sane to version 0.73.
* Update checksum.
* Update patches to patch against new sources.
* patch-03 no longer needed, it's now in the source.
* add new patch-04 to fix a new bogon.
* add instructions on how to configure it as a GIMP plug-in.
* redo PLIST to reflect the change in how libraries are installed
* add new man-page sane-microtek2.5 to both PLIST and Makefile
