* gegl/gegl-plugin.h: include operations/gegl-extension-handler.h as
well.
* operations/affine/module.c:
* operations/color/remap.c:
* operations/color/threshold.c:
* operations/color/value-invert.c:
* operations/core/clone.c:
* operations/core/crop.c:
* operations/core/nop.c:
* operations/core/shift.c:
* operations/io/load.c:
* operations/meta/layer.c:
* operations/render/introspect.c: modified to include an absolute
minimum of headers directly and rather include either gegl-plugin.h
or gegl-chant.h (which itself pulls in gegl-plugin.h, gegl-plugin.h
pulls in gegl.h for most of the gegl related environment and adds
the extra APIs provided for operation plug-ins.

svn path=/trunk/; revision=1887