pgsql: Add support for converting binary values (i.e.

Log Message:
-----------
Add support for converting binary values (i.e. bytea) into xml values,
with new GUC parameter "xmlbinary" that controls the output encoding, as
per SQL/XML standard.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        config.sgml (r1.102 -> r1.103)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml.diff?r1=1.102&r2=1.103)
    pgsql/src/backend/utils/adt:
        xml.c (r1.18 -> r1.19)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/xml.c.diff?r1=1.18&r2=1.19)
    pgsql/src/backend/utils/misc:
        guc.c (r1.368 -> r1.369)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c.diff?r1=1.368&r2=1.369)
    pgsql/src/include/utils:
        xml.h (r1.10 -> r1.11)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/xml.h.diff?r1=1.10&r2=1.11)
    pgsql/src/test/regress/expected:
        xml.out (r1.8 -> r1.9)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/xml.out.diff?r1=1.8&r2=1.9)
        xml_1.out (r1.8 -> r1.9)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/xml_1.out.diff?r1=1.8&r2=1.9)
    pgsql/src/test/regress/sql:
        xml.sql (r1.7 -> r1.8)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/xml.sql.diff?r1=1.7&r2=1.8)