Log Message:
-----------
Downgrade can't-happen error reports to elog().
Modified Files:
--------------
pgsql/src/backend/utils/time:
snapmgr.c (r1.5 -> r1.6)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/time/snapmgr.c?r1=1.5&r2=1.6)