minor, rewrite dt_dtdiff() to do a split dt_tdiff()+dt_ddiff() for all but t-only and d-only type combinations
minor, rewrite dt_dtdiff() to do a split dt_tdiff()+dt_ddiff() for all but t-only and d-only type combinations

Signed-off-by: Sebastian Freundt <1f0829204b3475c52f714f96be4e7b39a87b6e74@ga-group.nl>

rudimeier/dateutils,rudimeier/dateutils,rudimeier/dateutils