Three functionalities in one commit, but there's overlap so I can't

separate it...

1) Curve/Surface editmode undo
Uses same syntax as mesh undo, so simple to integrate. Edit-curve data is
also quite simpler, so no need for any hack at all.
It re-uses the undo system from next point, which is nice short & clean
local code

2) Framework for global undo
The undo calls themselves are commented out. In a next commit I want to
enable it for a couple of main features, for further feedback.
The speed goes surprisingly well, especially with this new version that
'pushes' undo after a command, ensuring interactivity isnt frustrated

3) framework for texture based icons in Blender
Not activated code, but tested here. Part of 2.3 UI project.

btw: Johnny Matthews will assist in (and complete) the undo project

source/blender/include/interface.h

@@ -209,7 +209,8 @@ extern void ui_window_to_graphics(int win, float *x, float *y);
 /* interface_panel.c */
 extern void ui_draw_panel(uiBlock *block);
 extern void ui_do_panel(uiBlock *block, uiEvent *uevent);
-extern void gl_round_box(float minx, float miny, float maxx, float maxy, float rad);
+extern void gl_round_box(int mode, float minx, float miny, float maxx, float maxy, float rad);
+extern void gl_round_box_shade(int mode, float minx, float miny, float maxx, float maxy, float rad, float shade);
 
 /* interface_draw.c */
 extern void ui_set_embossfunc(uiBut *but, int drawtype);