* app/paint_funcs.c: Shaved about 25% off the time spent in
combine_inten_[a_]and_inten_a_pixels() - yay.
* app/xcf.c: Removed 'M' and '.' debugging spew
* app/tile_manager.c: Removed #include <stdio.h>
* app/paint_funcs.c:
Fixed copy-on-write path of copy_region which was sometimes
crashing with Scott's new tile scheme.
* app/tile_manager.c:
Added some sanity warnings.
* app/xcf.c:
Fixed copy-on-write tile loading which was causing crashes
with Scott's new tile scheme. Ref balance count seems funny
still.