Log Message:
-----------
Add a comment about why we always replay backup blocks from WAL.
Modified Files:
--------------
pgsql-server/src/backend/access/transam:
xlog.c (r1.156 -> r1.157)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/access/transam/xlog.c.diff?r1=1.156&r2=1.157)