pgsql: Prevent ALTER USER f RESET ALL from removing the settings that

Log Message:
-----------
Prevent ALTER USER f RESET ALL from removing the settings that were put there
by a superuser -- "ALTER USER f RESET setting" already disallows removing such a
setting.

Apply the same treatment to ALTER DATABASE d RESET ALL when run by a database
owner that's not superuser.

Tags:
----
REL8_1_STABLE

Modified Files:
--------------
pgsql/src/backend/commands:
dbcommands.c (r1.173.2.3 -> r1.173.2.4)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/dbcommands.c?r1=1.173.2.3&r2=1.173.2.4)
user.c (r1.164 -> r1.164.2.1)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/user.c?r1=1.164&r2=1.164.2.1)
pgsql/src/backend/utils/misc:
guc.c (r1.299.2.8 -> r1.299.2.9)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c?r1=1.299.2.8&r2=1.299.2.9)
pgsql/src/include/utils:
guc.h (r1.63.2.2 -> r1.63.2.3)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/guc.h?r1=1.63.2.2&r2=1.63.2.3)