Condensed flag-setting code and put parantheses in the appropriate places.  It was that, in the end.

Set flag bits *exactly* as Andreas showed me in his screenshot.  This shouldn't be different, but what do I know about C's order of operations?

Mostly seem to have fixed SDL_CalculateShapeTree.  Mostly.  There still seem to be some rendering artifacts, stepping effects, and such on Windows -- which indicates subtle logic errors in SDL_CalculateShapeTree().

Oh well, back into the salt mine.

Reformatting code to match the rest of SDL.  Variable names seem OK; replaced tabs with 4 spaces each for indentation.

Fixed lots of little bugs in Win32 shaping and in SDL_CalculateShapeTree().  Still not actually showing anything on Windows, though there's no crashes and everything compiles fine.  Bugger.

Shaped windows for Cocoa build and testshape runs, but the actual shaping doesn't work.  Something, however, is definitely happening, because we get the backgrounds drawn in two different colors.