Do not double-subclass image windows after making a selection

oops
Do not show image tab strip in "floating images" mode
Increase opacity of "unsaved changes" icon.

I plan to improve the vibrance of it as well, but haven't done it just
yet.
Do not restrict image windows to main window if toolbars are floating

When both toolbars and images are floating, the user can now move things
wherever the hell they want.  If toolbars are docked, images remain
restricted to the main canvas, in MDI-like fashion.

Also, plain "move" and "size" events are now subclassed, and window
position automatically updated from them.  This fixes a number of
peripheral issues where external functions (like "Fit window to
viewport") were moving image windows but not updating their offset with
the window manager.
Uncheck "filled histogram curves" by default on XP

GDI+'s line function is simply too slow on XP.