pgsql: Fix SQL3 type return value.

Log Message:
-----------
Fix SQL3 type return value.

For non-SQL3 types ecpg used to return -Oid. This will break if there are
enough Oids to fill the namespace. Therefore we play it safe and return 0 if
there is no Oid->SQL3 tyoe mapping available.

Modified Files:
--------------
    pgsql/src/interfaces/ecpg/ecpglib:
        typename.c (r1.16 -> r1.17)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/ecpglib/typename.c?r1=1.16&r2=1.17)
    pgsql/src/interfaces/ecpg/test/expected:
        sql-dyntest.c (r1.22 -> r1.23)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/expected/sql-dyntest.c?r1=1.22&r2=1.23)
        sql-dyntest.stderr (r1.11 -> r1.12)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/expected/sql-dyntest.stderr?r1=1.11&r2=1.12)
        sql-dyntest.stdout (r1.3 -> r1.4)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/expected/sql-dyntest.stdout?r1=1.3&r2=1.4)
    pgsql/src/interfaces/ecpg/test/sql:
        dyntest.pgc (r1.7 -> r1.8)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/sql/dyntest.pgc?r1=1.7&r2=1.8)