Fix the problem that clean_canvas() can not clean canvas cleanly. - For some unknown reasons, cairo_paint() can not clean painted graphics cleanly. - Use cairo_rectangle() and cairo_fill() to replace cairo_paint().

include_HEADERS = 	\
	mb_animate.h 	\
	mb.h	 	\
	mb_timer.h 	\
	mb_types.h 	\
	mb_observer.h	\
	mb_paint.h	\
	mb_redraw_man.h	\
	mb_shapes.h	\
	mb_tools.h	\
	mb_prop.h	\
	mb_X_supp.h	\
	mb_so.h