pgsql: Fix bug in SET SESSION AUTHORIZATION that allows unprivileged

Log Message:
-----------
Fix bug in SET SESSION AUTHORIZATION that allows unprivileged users to crash
the server, if it has been compiled with Asserts enabled (CVE-2006-0553).
Thanks to Akio Ishida for reporting this problem.

Tags:
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REL7_4_STABLE

Modified Files:
--------------
    pgsql/src/backend/commands:
        variable.c (r1.88.2.2 -> r1.88.2.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/variable.c.diff?r1=1.88.2.2&r2=1.88.2.3)
    pgsql/src/backend/utils/mb:
        encnames.c (r1.17 -> r1.17.4.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/mb/encnames.c.diff?r1=1.17&r2=1.17.4.1)
    pgsql/src/backend/utils/misc:
        guc.c (r1.164.2.3 -> r1.164.2.4)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c.diff?r1=1.164.2.3&r2=1.164.2.4)
    pgsql/src/include/utils:
        guc_tables.h (r1.6 -> r1.6.4.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/guc_tables.h.diff?r1=1.6&r2=1.6.4.1)