Gegl build failures

[Andreas Enge]

gegl, an input for gimp, fails its tests:
   http://hydra.gnu.org/build/159641/nixlog/1/tail-reload

We already have the following comments in the package:
          ;; This test program seems to crash on exit. Specifically, whilst
          ;; g_object_unreffing bufferA and bufferB - This seems to be a bug
          ;; in the destructor.  This is just a test program so will not have
          ;; any wider effect, although might be hiding another problem.
          ;; According to advice received on irc.gimp.org#gegl although 0.2.0
          ;; is the latest released version, any bug reports against it will
          ;; be ignored.  So we are on our own.
before a line that removes one test. I would suggest to disable all tests.

Andreas