pgsql: The session_replication_role actually can be changed at will

Log Message:
-----------
The session_replication_role actually can be changed at will during
a session regardless of the existence of cached plans. The plancache
only needs to be invalidated so that rules affected by the new setting
will be reflected in the new query plans.

Jan

Modified Files:
--------------
    pgsql/src/backend/utils/cache:
        plancache.c (r1.9 -> r1.10)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/cache/plancache.c.diff?r1=1.9&r2=1.10)
    pgsql/src/backend/utils/misc:
        guc.c (r1.393 -> r1.394)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c.diff?r1=1.393&r2=1.394)
    pgsql/src/include/utils:
        plancache.h (r1.6 -> r1.7)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/plancache.h.diff?r1=1.6&r2=1.7)