Instead of having BABL_CLASS() plus variants and making the macros

Instead of having BABL_CLASS() plus variants and making the macros
expand to different things depending on if they are used in a
header or a .c file, have two versions: BABL_CLASS_DECLARE() and
BABL_CLASS_IMPLEMENT(). This enables further refactorisations of
the babl.h header.

* babl.h: Do the name changes and remove the unpleasant #undefs at
the bottom.

* babl-internal.h: Do the name changes.

* babl-component.[ch]
* babl-conversion.[ch]
* babl-extension.[ch]
* babl-fish.[ch]
* babl-format.[ch]
* babl-image.h
* babl-model.[ch]
* babl-sampling.h
* babl-type.[ch]: Adjust to changes.

svn path=/trunk/; revision=370