pgsql: Add xmlexists function by Mike Fowler, reviewed by Peter

Log Message:
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Add xmlexists function

by Mike Fowler, reviewed by Peter Eisentraut

Modified Files:
--------------
pgsql/doc/src/sgml:
func.sgml (r1.522 -> r1.523)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml?r1=1.522&r2=1.523)
pgsql/src/backend/parser:
gram.y (r2.714 -> r2.715)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y?r1=2.714&r2=2.715)
pgsql/src/backend/utils/adt:
xml.c (r1.98 -> r1.99)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/xml.c?r1=1.98&r2=1.99)
pgsql/src/include/catalog:
catversion.h (r1.588 -> r1.589)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h?r1=1.588&r2=1.589)
pg_proc.h (r1.573 -> r1.574)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h?r1=1.573&r2=1.574)
pgsql/src/include/parser:
kwlist.h (r1.12 -> r1.13)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/parser/kwlist.h?r1=1.12&r2=1.13)
pgsql/src/include/utils:
xml.h (r1.31 -> r1.32)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/xml.h?r1=1.31&r2=1.32)
pgsql/src/test/regress/expected:
xml.out (r1.25 -> r1.26)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/xml.out?r1=1.25&r2=1.26)
xml_1.out (r1.26 -> r1.27)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/xml_1.out?r1=1.26&r2=1.27)
pgsql/src/test/regress/sql:
xml.sql (r1.19 -> r1.20)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/xml.sql?r1=1.19&r2=1.20)