pgsql: Fix xmlattribute escaping XML special characters twice (bug

Log Message:
-----------
Fix xmlattribute escaping XML special characters twice (bug #4822).

Author: Itagaki Takahiro <itagaki.takahiro@oss.ntt.co.jp>

Modified Files:
--------------
    pgsql/src/backend/executor:
        execQual.c (r1.247 -> r1.248)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execQual.c?r1=1.247&r2=1.248)
    pgsql/src/backend/utils/adt:
        xml.c (r1.89 -> r1.90)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/xml.c?r1=1.89&r2=1.90)
    pgsql/src/include/utils:
        xml.h (r1.26 -> r1.27)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/xml.h?r1=1.26&r2=1.27)
    pgsql/src/test/regress/expected:
        xml.out (r1.24 -> r1.25)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/xml.out?r1=1.24&r2=1.25)
        xml_1.out (r1.25 -> r1.26)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/xml_1.out?r1=1.25&r2=1.26)
    pgsql/src/test/regress/sql:
        xml.sql (r1.18 -> r1.19)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/xml.sql?r1=1.18&r2=1.19)