* gegl/buffer/gegl-buffer-access.c:
(gegl_buffer_tile_iterator_init), (gegl_buffer_scan_iterator_init),
(gegl_buffer_scan_iterator_next), (gegl_buffer_tile_iterator_next):
modified to make the roi for the scan iterator reported be correct.
* gegl/buffer/gegl-buffer-private.h: modified computation of roi.
* gegl/operation/gegl-operation-point-render.c: override some of the
base source op's modifications of base operation wrt caching.
* operations/common/checkerboard.c: port to be subclass of
point-render.
* operations/common/color.c: (gegl_chant_class_init): removed
initialization now moved to base class.

svn path=/trunk/; revision=2367