* app/brightness_contrast.c
	* app/by_color_select.c
	* app/color_balance.c
	* app/color_picker.c
	* app/curves.c
	* app/histogram_tool.c
	* app/hue_saturation.c
	* app/levels.c
	* app/posterize.c
	* app/threshold.c
	* app/transform_core.c: modified to call the cancel callback
	instead of the ok callback when freed.  modified to save the
	last used drawable so that we might be able to check later
	and restart the tool if need be.

	* app/disp_callbacks.c
	* app/gimage.c: modified tool restart/destruction code

	* app/tools.c
	* app/tools.h: added tools_initialize, made changes to
	be able save the last used drawable in the tool.

--Matt