[gimp] app: disable multi-threading on "gimp:shapeburst" operation.

[Jehan Pagès <jehanp src gnome org>]

commit 6f127f9db43c081f7ad5c217f43e6d6714cecf86
Author: Jehan <jehan girinstud io>
Date:   Tue Mar 13 18:20:16 2018 +0100

    app: disable multi-threading on "gimp:shapeburst" operation.
    
    This operation is currently broken on multi-thread. So disable
    multi-threading, at least temporarily (if not forever since apparently
    we can get similar output with "gegl:distance-transform", but much
    faster and nicer). See bug 781621.

 app/operations/gimpoperationshapeburst.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/app/operations/gimpoperationshapeburst.c b/app/operations/gimpoperationshapeburst.c
index 0440bb6..f71c018 100644
--- a/app/operations/gimpoperationshapeburst.c
+++ b/app/operations/gimpoperationshapeburst.c
@@ -88,6 +88,10 @@ gimp_operation_shapeburst_class_init (GimpOperationShapeburstClass *klass)
   operation_class->prepare                 = gimp_operation_shapeburst_prepare;
   operation_class->get_required_for_output = gimp_operation_shapeburst_get_required_for_output;
   operation_class->get_cached_region       = gimp_operation_shapeburst_get_cached_region;
+  /* This operation is currently broken when multi-threaded.
+   * Cf. bug 781621. FIXME.
+   */
+  operation_class->threaded                = FALSE;
 
   filter_class->process                    = gimp_operation_shapeburst_process;