Log Message:
-----------
Add a comment describing the requirement that pointers into shared memory
that is protected by a spinlock must be volatile, per recent discussion.
Modified Files:
--------------
pgsql/src/include/storage:
spin.h (r1.25 -> r1.26)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/spin.h.diff?r1=1.25&r2=1.26)