enable seq for colourspace

TODO

@@ -1,7 +1,12 @@
+
 - use D65 in cmsCreateLab4Profile() ? not sure
 
 - the operation cache needs to detect invalidate
 
+- move resample part of transform plugin into libvips
+
+- check CMC equations against web
+
 - see
 
         http://www.dentistry.bham.ac.uk/landinig/software/cdeconv/cdeconv.html

libvips/colour/colourspace.c

@@ -288,6 +288,7 @@ vips_colourspace_class_init( VipsColourspaceClass *class )
 {
 	GObjectClass *gobject_class = G_OBJECT_CLASS( class );
 	VipsObjectClass *vobject_class = VIPS_OBJECT_CLASS( class );
+	VipsOperationClass *operation_class = VIPS_OPERATION_CLASS( class );
 
 	gobject_class->set_property = vips_object_set_property;
 	gobject_class->get_property = vips_object_get_property;
@@ -296,6 +297,8 @@ vips_colourspace_class_init( VipsColourspaceClass *class )
 	vobject_class->description = _( "convert to a new colourspace" );
 	vobject_class->build = vips_colourspace_build;
 
+	operation_class->flags = VIPS_OPERATION_SEQUENTIAL;
+
 	VIPS_ARG_IMAGE( class, "in", 1, 
 		_( "Input" ), 
 		_( "Input image" ),