pgsql: array_agg aggregate function, as per SQL:2008, but without ORDER

Log Message:
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array_agg aggregate function, as per SQL:2008, but without ORDER BY clause

Rearrange the documentation a bit now that array_agg and xmlagg have similar
semantics and issues.

best of Robert Haas, Jeff Davis, Peter Eisentraut

Modified Files:
--------------
pgsql/doc/src/sgml:
func.sgml (r1.457 -> r1.458)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml?r1=1.457&r2=1.458)
pgsql/src/backend/catalog:
sql_features.txt (r1.31 -> r1.32)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/sql_features.txt?r1=1.31&r2=1.32)
pgsql/src/backend/utils/adt:
array_userfuncs.c (r1.23 -> r1.24)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/array_userfuncs.c?r1=1.23&r2=1.24)
pgsql/src/include/catalog:
catversion.h (r1.504 -> r1.505)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h?r1=1.504&r2=1.505)
pg_aggregate.h (r1.66 -> r1.67)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_aggregate.h?r1=1.66&r2=1.67)
pg_proc.h (r1.526 -> r1.527)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h?r1=1.526&r2=1.527)
pgsql/src/include/utils:
array.h (r1.70 -> r1.71)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/array.h?r1=1.70&r2=1.71)
pgsql/src/test/regress/expected:
arrays.out (r1.43 -> r1.44)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/arrays.out?r1=1.43&r2=1.44)
pgsql/src/test/regress/sql:
arrays.sql (r1.32 -> r1.33)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/arrays.sql?r1=1.32&r2=1.33)