* app/gimplut.[ch]: new source files that implement pixel Look Up
 	Table functions.

	* app/Makefile.am: build gimplut.[ch]


	* app/brightness_contrast.c
	* app/curves.c
	* app/invert.c
	* app/levels.c
	* app/posterize.c: Use the new lut functions.  Use
 	pixel_region_process_parallel in the PDB versions of these routines.

	* libgimp/parasite.h
	* libgimp/parasite.c: new functions parasite_name and
 	parasite_compare.

	* app/gimpdrawable.c:
	* app/gimpdrawable.h: new function
 	gimp_drawable_get_color_at(...) returns the RGBA[color index]
 	value at a specified position in the drawable.  Don't set the dirty
 	bit on the image if a new parasite is the same as the old.

	* app/gimpimage.c
	* app/gimpimage.h new function
 	gimp_image_get_color_at(...) returns the RGBA[color index]
 	value at a specified position in the drawable.  Don't set the dirty
 	bit on the image if a new parasite is the same as the old.

	* app/by_color_select.c
	* app/color_picker.c: use the new gimp_*_get_color_at
 	functions instead of messing with the tiles.

	* app/layer.c: fixed a minor warning.

	* app/commands.c:
	don't scale the image if the new size == the old size

	* app/channel.c: optimized channel_bounds by only checking the
 	pixels in a tile if it is not already entirely within the
 	currently computed bounds.