Support for displaying PNG images in Tioga !

git-svn-id: svn+ssh://rubyforge.org/var/svn/tioga/trunk/tioga@643 f6f669a6-2b79-499e-8f05-be2b991fc3d0
First step in refactoring the image display to make it possible to use image objects several times

git-svn-id: svn+ssh://rubyforge.org/var/svn/tioga/trunk/tioga@644 f6f669a6-2b79-499e-8f05-be2b991fc3d0
Next step: use the new scheme internally for private_show_image

git-svn-id: svn+ssh://rubyforge.org/var/svn/tioga/trunk/tioga@645 f6f669a6-2b79-499e-8f05-be2b991fc3d0
Make use of c_private_show_image_from_ref also for JPEG images

git-svn-id: svn+ssh://rubyforge.org/var/svn/tioga/trunk/tioga@646 f6f669a6-2b79-499e-8f05-be2b991fc3d0
New scheme for the all the images: first registration, then use

This change is transparent for the old code

git-svn-id: svn+ssh://rubyforge.org/var/svn/tioga/trunk/tioga@647 f6f669a6-2b79-499e-8f05-be2b991fc3d0
New figure in the samples using the reference

git-svn-id: svn+ssh://rubyforge.org/var/svn/tioga/trunk/tioga@648 f6f669a6-2b79-499e-8f05-be2b991fc3d0
Documentation for the newly created image functions

git-svn-id: svn+ssh://rubyforge.org/var/svn/tioga/trunk/tioga@649 f6f669a6-2b79-499e-8f05-be2b991fc3d0