pgsql: Add xml_is_well_formed, xml_is_well_formed_document,

Log Message:
-----------
Add xml_is_well_formed, xml_is_well_formed_document, xml_is_well_formed_content
functions to the core XML code. Per discussion, the former depends on
XMLOPTION while the others do not. These supersede a version previously
offered by contrib/xml2.

Mike Fowler, reviewed by Pavel Stehule

Modified Files:
--------------
pgsql/contrib/xml2:
pgxml.sql.in (r1.12 -> r1.13)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/xml2/pgxml.sql.in?r1=1.12&r2=1.13)
uninstall_pgxml.sql (r1.4 -> r1.5)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/xml2/uninstall_pgxml.sql?r1=1.4&r2=1.5)
xpath.c (r1.30 -> r1.31)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/xml2/xpath.c?r1=1.30&r2=1.31)
pgsql/doc/src/sgml:
func.sgml (r1.526 -> r1.527)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml?r1=1.526&r2=1.527)
pgsql/src/backend/utils/adt:
xml.c (r1.100 -> r1.101)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/xml.c?r1=1.100&r2=1.101)
pgsql/src/include/catalog:
catversion.h (r1.594 -> r1.595)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h?r1=1.594&r2=1.595)
pg_proc.h (r1.578 -> r1.579)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h?r1=1.578&r2=1.579)
pgsql/src/include/utils:
xml.h (r1.33 -> r1.34)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/xml.h?r1=1.33&r2=1.34)
pgsql/src/test/regress/expected:
xml.out (r1.27 -> r1.28)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/xml.out?r1=1.27&r2=1.28)
xml_1.out (r1.28 -> r1.29)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/xml_1.out?r1=1.28&r2=1.29)
pgsql/src/test/regress/sql:
xml.sql (r1.21 -> r1.22)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/xml.sql?r1=1.21&r2=1.22)