[gui] [patch] somewhat disruptive, big patch

[graydon hoare]

hi,

I've just committed this rather disruptive patch. It began with a need 
to get the viewport and scrollpane stuff worked out, then digressed into 
getting the repainting cycle (repaint manager and jcomponent) working 
properly, then cairo's API shifted and I had to adjust to that, which 
exposed more cairo bugs which I had to work around (and put some 
checking mechanisms in place to prevent).

http://people.redhat.com/graydon/j2d-repaintmanager-and-jcomponent-rewrite.patch

in the end, the viewport and scrollpane stuff is only half working, but 
I figured it was time to settle things down and commit all the other 
housekeeping.

so, unfortunately this is large. it will probably perturb some existing 
tests. it also makes the swing painting system "work" the way it's 
supposed to: paints and validations are done by the painting thread, in 
a coalesced batch, with a clipped, double-buffered offscreen painting 
region, shared across the component tree.

this has been holding up a lot of other work. sorry. I will commence the 
supposed-to-be-monthly GUI -> trunk merge shortly.

-graydon