Postgres: use lastval() to retrieve last insert id
Postgres: use lastval() to retrieve last insert id

Reverting change from d01454c0bf608ecd6625ccd9d968d45af7adac4c which
introduced a regression.

Fixes #8

pyscht/ADOdb,azghanvi/ADOdb,azghanvi/ADOdb,paulproteus/ADOdb,andrewnicols/ADOdb,pyscht/ADOdb,paulproteus/ADOdb,ipso/ADOdb,ipso/ADOdb,andrewnicols/ADOdb