* app/bezier_select.c: Destroy the tool when changing displays.
	* app/command.c: initialize pointers to drawables when selecting
	tools
	* app/disp_callbacks.c: initialize pointers to drawables on first
	click of a gdisplay
	* app/gimage.c: removed extra tool destruction
	* app/tools.c: make a fallback case when starting tools so that
	you'll always have an active tool.

--Matt