pgsql: Fix bug that allowed any logged-in user to SET ROLE to any other

Log Message:
-----------
Fix bug that allowed any logged-in user to SET ROLE to any other database user
id (CVE-2006-0553). Also fix related bug in SET SESSION AUTHORIZATION that
allows unprivileged users to crash the server, if it has been compiled with
Asserts enabled. The escalation-of-privilege risk exists only in 8.1.0-8.1.2.
However, the Assert-crash risk exists in all releases back to 7.3.
Thanks to Akio Ishida for reporting this problem.

Tags:
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REL8_1_STABLE

Modified Files:
--------------
pgsql/src/backend/commands:
variable.c (r1.114.2.1 -> r1.114.2.2)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/variable.c.diff?r1=1.114.2.1&r2=1.114.2.2)
pgsql/src/backend/utils/mb:
encnames.c (r1.26 -> r1.26.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/mb/encnames.c.diff?r1=1.26&r2=1.26.2.1)
pgsql/src/backend/utils/misc:
guc.c (r1.299.2.1 -> r1.299.2.2)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c.diff?r1=1.299.2.1&r2=1.299.2.2)
pgsql/src/include/utils:
guc_tables.h (r1.20 -> r1.20.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/guc_tables.h.diff?r1=1.20&r2=1.20.2.1)