Whirlpool, Subterranean Gates, and all Monoliths now show custom popup
on right-click that show all linked objects (exits and entrances).
Only revealed objects are visible, rest are hidden behind fow.
Exits, entrances, and bidirectional objects have different icon that
indicates direction.
- added compatibility method to Canvas to allow SDL_Surface access
- added drawBorder method to Canvas to replace CSDL_Ext method
- added drawColor method to Canvas to replace CSDL_Ext method
- minor changes to Tavern and Trade windows to adapt to new API
