1999-06-23  Michael Natterer  <mitschel@cs.tu-berlin.de>

	* app/brightness_contrast.c
	* app/by_color_select.c
	* app/curves.c
	* app/disp_callbacks.c
	* app/histogram_tool.c
	* app/hue_saturation.c
	* app/levels.c
	* app/posterize.c
	* app/threshold.c:

	Factored out the cleaning up code to the tool dialog's "cancel"
	callbacks because they are called from every function which is
	aborting the tool. This should fix the remaining segfaults.

	I probably killed a feature of "Levels". The tool wanted to
	preserve it's drawable all the time, so it was possible to select
	colors from other displays. If this was the intended behaviour,
	please flame me and I will try to set the "preserve" flag
	correctly.

	* plug-ins/common/Makefile.am: "struc" was in the Makefile but not
	in the directory.