* 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.
