small graphics fixes

[Shai Ayal]

I attach a changeset with 3 small changes:
1. typo fix
2. change rendering order in gl-renderer so that the list of children
is drawn from end to start -- the first child in the list should  be
on top of the others
3. change colorbar from an image to a surface. while using an image is
more concise, using a surface has the advantage of working with the
current gl-renderer, and with gl2ps, so that it will appear in the
postscript output.

I plan to begin indexed image support in the gl-renderer (but I'm
afraid it will still have problems converting to postscript).
Also, a lot of graphics scripts are not backend-agnostic and contain
many gnuplot specifics -- most notably. print.m I think they should be
seperated into backend specific and backend agnostic parts. I will try
to do this myself, but any help would be appreciated.

Shai

various_graphics.changeset
Description: Binary data