pgsql: XMLATTRIBUTES() should send the attribute values through

Log Message:
-----------
XMLATTRIBUTES() should send the attribute values through
map_sql_value_to_xml_value() instead of directly through the data type output
function.  This is per SQL standard, and consistent with XMLELEMENT().

Modified Files:
--------------
    pgsql/src/backend/executor:
        execQual.c (r1.245 -> r1.246)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execQual.c?r1=1.245&r2=1.246)
    pgsql/src/backend/utils/adt:
        xml.c (r1.85 -> r1.86)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/xml.c?r1=1.85&r2=1.86)
    pgsql/src/include/nodes:
        execnodes.h (r1.203 -> r1.204)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/execnodes.h?r1=1.203&r2=1.204)
    pgsql/src/test/regress/expected:
        xml.out (r1.23 -> r1.24)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/xml.out?r1=1.23&r2=1.24)
        xml_1.out (r1.24 -> r1.25)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/xml_1.out?r1=1.24&r2=1.25)
    pgsql/src/test/regress/sql:
        xml.sql (r1.17 -> r1.18)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/xml.sql?r1=1.17&r2=1.18)