3900. [bug] Fix a crash in PostgreSQL DLZ driver. [RT #36637]

3900.  [bug]           Fix a crash in PostgreSQL DLZ driver. [RT #36637]

Squashed commit of the following:

commit ebdade4dfe59fc11d3c4ad8111729f722aab2008
Author: Mukund Sivaraman <muks@isc.org>
Date:   Thu Jul 24 22:52:54 2014 +0530

    Move statement to be after comment

commit 4b5d6a33350a469afb8e273bc552055824a32570
Author: Mukund Sivaraman <muks@isc.org>
Date:   Thu Jul 24 21:42:52 2014 +0530

    Return NULL in *rs so that caller doesn't PQclear() it again

(cherry picked from commit 586db4a3e4664109fe8ce31fdd6a1b9c5bb67cbf)