2004-06-16  Michael Natterer  <mitch@gimp.org>

	Started to fix bug #106920 in a more genreral way:

	* libgimpwidgets/Makefile.am
	* libgimpwidgets/gimpwidgetstypes.h
	* libgimpwidgets/gimpwidgetsmarshal.list
	* libgimpwidgets/gimpcontroller.[ch]: new abstract base class
	which provides an API for pluggable input controller modules
	(mouse wheel, usb/midi stuff etc.).

	* app/widgets/Makefile.am
	* app/widgets/widgets-types.h
	* app/widgets/gimpcontrollerwheel.[ch]: subclass of the above
	which maps wheel mouse scroll events to controller events.

	* app/widgets/gimpcontrollers.[ch]: manager for controllers.
	reads $(gimpdir)/controllerrc and keeps a mapping of controller
	events to GtkActions.

	* app/gui/gui.c: initialize and shut down the controller stuff.

	* app/display/gimpdisplayshell-callbacks.c
	(gimp_display_shell_canvas_tool_events): if a wheel controller
	exists, dispatch GdkEventScroll to it first and return if it was
	handled.