on CORE previously.

This module offers transaction ID's containing the original XID and the
transaction epoch as a bigint value to the user level. It also provides
a special txid_snapshot data type that contains an entire transactions
visibility snapshot information, which is useful to determine if a
particular txid was visible to a transaction or not.

The module has been tested by porting Slony-I from using its original
xxid data type.

Jan