[SQLObject] _fromDatabase for Postgres

Are there any plans afoot to add this support for Postgres?  I know how to
get the info out of the Postgres system tables, so it looks like the
columnsFromSchema would not be hard to implement for PosgresConnection, but
what else might be involved?  Well, I'm going to try dinking with it a bit
anyway, so we'll see what happens.

Dave Cook