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}
Deactivate compatibility with versions before OpenACS 5.2 (2005) in busy code, but leave it there commented out for easy reactivating in legacy applications.