Provide an exception in case get_instance_from_db is called with an invalid argument combination. Added convenience methods "::xo::db::CrClass->ensure_item_ids_instantiated"
performance improvements for "::xo::db::Class proc get_instance_from_db"
when the object exists already, the text for existance is made earlier to void useless operations. This change improves the performance by a factor of 3 when the object was already loaded.
OLD {4.544836 microseconds per iteration} NEW {1.310991 microseconds per iteration}