SIGABRT is definitely a fatal error, at least in GIMP context. It is
used by g_assert() and more generally by abort().

Actually I am a bit unsure about the difference of gimp_terminate() and
gimp_fatal_error(). The former mostly depends on whether we used
--debug-handlers or not, which reads "Enable non-fatal debugging signal
handlers". But the way we handle them, the list of signals handled by
gimp_terminate() seem to always end up fatal as well, anyway. So either
we should *really* make them non-fatal (I could imagine that SIGTERM or
SIGINT indeed could be better handled for instance), or we should just
get rid of this terminate/fatal_error differentiation which seems
totally artificial and non-existing in the current code.