pgsql: Added variable handling for RETURNING clause to ecpg.

Log Message:
-----------
Added variable handling for RETURNING clause to ecpg.

While the values were correctly returned they were not moved into C variables
as they should be.

Closes: #5489

Modified Files:
--------------
    pgsql/src/interfaces/ecpg/preproc:
        parse.pl (r1.8 -> r1.9)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/preproc/parse.pl?r1=1.8&r2=1.9)
    pgsql/src/interfaces/ecpg/test/expected:
        sql-insupd.c (r1.7 -> r1.8)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/expected/sql-insupd.c?r1=1.7&r2=1.8)
        sql-insupd.stderr (r1.8 -> r1.9)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/expected/sql-insupd.stderr?r1=1.8&r2=1.9)
        sql-insupd.stdout (r1.1 -> r1.2)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/expected/sql-insupd.stdout?r1=1.1&r2=1.2)
    pgsql/src/interfaces/ecpg/test/sql:
        insupd.pgc (r1.3 -> r1.4)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/sql/insupd.pgc?r1=1.3&r2=1.4)