pgsql: Regression test for XML mapping functionality I wrote this one

Log Message:
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Regression test for XML mapping functionality

I wrote this one while chasing down some bugs in the closing days of 8.4. It
could be useful in the long run. This area of the code had no test coverage
at all before.

Modified Files:
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pgsql/src/test/regress:
parallel_schedule (r1.55 -> r1.56)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/parallel_schedule?r1=1.55&r2=1.56)
serial_schedule (r1.52 -> r1.53)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/serial_schedule?r1=1.52&r2=1.53)

Added Files:
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pgsql/src/test/regress/expected:
xmlmap.out (r1.1)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/xmlmap.out?rev=1.1&content-type=text/x-cvsweb-markup)
xmlmap_1.out (r1.1)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/xmlmap_1.out?rev=1.1&content-type=text/x-cvsweb-markup)
pgsql/src/test/regress/sql:
xmlmap.sql (r1.1)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/xmlmap.sql?rev=1.1&content-type=text/x-cvsweb-markup)