typing: reset tuple cache when adding props, too
typing: reset tuple cache when adding props, too

this fixes a problem with encoding_decorate, where
a parsed Prelude theory contained unneeded "use Tuple2"

douglas-larocca/why3,douglas-larocca/why3,ssaavedra/why3,jpdeplaix/why3,jpdeplaix/why3,ssaavedra/why3,jpdeplaix/why3,douglas-larocca/why3,ssaavedra/why3