2004-01-21  Michael Natterer  <mitch@gimp.org>

	* app/tools/gimptool.[ch]: added boolean return value to
	GimpTool::initialize(). Returning FALSE means the tool could not
	be initialized and doesn't want to receive button events.
	Return TRUE from the default implementation.

	* app/tools/tool_manager.[ch]: added boolean return value to
	tool_manager_initialize_active(). Don't set the tool's display or
	drawable if initialize() returns FALSE.

	* app/display/gimpdisplayshell-callbacks.c: don't send button
	events to the tool if initialize() returns FALSE.

	* app/tools/gimpbrightnesscontrasttool.c
	* app/tools/gimpcolorbalancetool.c
	* app/tools/gimpcolorizetool.c
	* app/tools/gimpcurvestool.c
	* app/tools/gimphuesaturationtool.c
	* app/tools/gimplevelstool.c
	* app/tools/gimpposterizetool.c
	* app/tools/gimpthresholdtool.c: return FALSE for NULL and indexed
	drawables.

	* app/tools/gimpimagemaptool.c: always return TRUE because our
	subclasses already checked if the active drawable is OK.

	* app/tools/gimptransformtool.c: return FALSE for layers with
	masks. Fixes bug #132089. Some random cleanups.