Log Message:
-----------
Improve documentation about how checkpoint spreads I/O activity.
Modified Files:
--------------
pgsql/doc/src/sgml:
wal.sgml (r1.58 -> r1.59)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/wal.sgml?r1=1.58&r2=1.59)