plpsm - plpgpsm: merge patch

Log Message:
-----------
merge patch http://archives.postgresql.org/pgsql-committers/2007-02/msg00016.php
not null domain check

Modified Files:
--------------
    plpgpsm/src:
        pl_exec.c (r1.31 -> r1.32)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/plpsm/plpgpsm/src/pl_exec.c.diff?r1=1.31&r2=1.32)
    plpgpsm/src/expected:
        plpgpsm.out (r1.6 -> r1.7)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/plpsm/plpgpsm/src/expected/plpgpsm.out.diff?r1=1.6&r2=1.7)
    plpgpsm/src/sql:
        plpgpsm.sql (r1.5 -> r1.6)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/plpsm/plpgpsm/src/sql/plpgpsm.sql.diff?r1=1.5&r2=1.6)