[Inkscape-devel] compiled-in paths

I moved the INKSCAPE_*DIR paths into config.h so that all subdirs would pick them up. This also makes it dependencies will be checked correctly if "configure" is re-run and paths change. Before, you could change the "prefix" and some .cpp files would not get recompiled with the new path.

Hopefully my logic is sane and I haven't horribly broken anything. It seems that either way (with Makefile -D's or with config.h #defines) the paths end up compiled in, so there's no difference other than better visibility to the defines.