* libgimpwidgets/gimppreview.[ch]: added a new function to set the
  default cursor on preview: gimp_preview_set_default_cursor().

* libgimpwidgets/gimpscrolledpreview.c: changed accordlingly.

* plug-ins/common/flarefx.c:
* plug-ins/common/nova.c: use this function.

This addresses bug #90519.