pgsql: Various fixes in the logic of XML functions: - Add new SQL

Log Message:
-----------
Various fixes in the logic of XML functions:

- Add new SQL command SET XML OPTION (also available via regular GUC) to
control the DOCUMENT vs. CONTENT option in implicit parsing and
serialization operations.

- Subtle corrections in the handling of the standalone property in
xmlroot().

- Allow xmlroot() to work on content fragments.

- Subtle corrections in the handling of the version property in
xmlconcat().

- Code refactoring for producing XML declarations.

Modified Files:
--------------
pgsql/doc/src/sgml:
config.sgml (r1.105 -> r1.106)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml.diff?r1=1.105&r2=1.106)
datatype.sgml (r1.185 -> r1.186)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/datatype.sgml.diff?r1=1.185&r2=1.186)
pgsql/src/backend/executor:
execQual.c (r1.208 -> r1.209)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execQual.c.diff?r1=1.208&r2=1.209)
pgsql/src/backend/parser:
gram.y (r2.576 -> r2.577)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y.diff?r1=2.576&r2=2.577)
keywords.c (r1.183 -> r1.184)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/keywords.c.diff?r1=1.183&r2=1.184)
parse_expr.c (r1.208 -> r1.209)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_expr.c.diff?r1=1.208&r2=1.209)
pgsql/src/backend/utils/adt:
xml.c (r1.21 -> r1.22)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/xml.c.diff?r1=1.21&r2=1.22)
pgsql/src/backend/utils/misc:
guc.c (r1.370 -> r1.371)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c.diff?r1=1.370&r2=1.371)
postgresql.conf.sample (r1.205 -> r1.206)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample.diff?r1=1.205&r2=1.206)
pgsql/src/include/utils:
xml.h (r1.12 -> r1.13)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/xml.h.diff?r1=1.12&r2=1.13)
pgsql/src/test/regress/expected:
xml.out (r1.12 -> r1.13)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/xml.out.diff?r1=1.12&r2=1.13)
xml_1.out (r1.10 -> r1.11)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/xml_1.out.diff?r1=1.10&r2=1.11)
pgsql/src/test/regress/sql:
xml.sql (r1.9 -> r1.10)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/xml.sql.diff?r1=1.9&r2=1.10)