* configure.ac: modified --enable-mp, it is now disabled by default.
* gegl/gegl-init.c: (gegl_init): initialize gthread if ENABLE_MP is
set.
* gegl/process/gegl-processor.c: (gegl_processor_work): do actual
processing in auxiliary thread (currently lacks sufficient locking to
work properly, but when it does work both the GEGL gui and GIMP are
more responsive.)

svn path=/trunk/; revision=2135