Fix Persistent compatibility

Bump minimum bounds because we cannot test Persistent 1.x.

Add the TypeSynonymInstances pragma, because Persistent 2.0.y does not
build without it, and newer Persistent doesn't really care either way.

Signed-off-by: Alexander Berntsen <alexander@plaimi.net>
Signed-off-by: Stian Ellingsen <stian@plaimi.net>
Reviewed-by: Stian Ellingsen <stian@plaimi.net>