added ability for type 1 scds to copy more data from original version
added ability for type 1 scds to copy more data from original version

Type 1 scds have always copied over the primary key, but now other things
can be copied over, by entering a :non_evolving_fields to the SCD parameters.

This seems to be useful for implementing aggregate snapshot facts, where some
fields are updated, and others remain the same.

activewarehouse/activewarehouse