Fix some additional cases of VACUUM "No one parent tuple was found" error

Prevent VACUUM from being called inside a function (Bruce)

Ensure pg_clog updates are sync'd to disk before marking checkpoint complete

Avoid integer overflow during large hash joins

Make GROUP commands work when pg_group.grolist is large enough to be toasted

Fix errors in datetime tables; some timezone names weren't being recognized

Fix integer overflows in circle_poly(), path_encode(), path_add() (Neil)

Repair long-standing logic errors in lseg_eq(), lseg_ne(), lseg_center()