pgsql: Minor correction: cause ALTER ROLE role ROLE rolenames to behave

[tgl(at)svr1(dot)postgresql(dot)org (Tom Lane)]

Log Message:
-----------
Minor correction: cause ALTER ROLE role ROLE rolenames to behave
sensibly, even though we don't document it.

Modified Files:
--------------
    pgsql/src/backend/commands:
        user.c (r1.158 -> r1.159)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/user.c.diff?r1=1.158&r2=1.159)
    pgsql/src/backend/parser:
        gram.y (r2.503 -> r2.504)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y.diff?r1=2.503&r2=2.504)