DOC: Wal update

I add few sentences how to write cache works on Solaris platform.


        Zdenek
Index: doc/src/sgml/wal.sgml
===================================================================
RCS file: /zfs_data/cvs_pgsql/cvsroot/pgsql/doc/src/sgml/wal.sgml,v
retrieving revision 1.49
diff -c -r1.49 wal.sgml
*** doc/src/sgml/wal.sgml    10 Dec 2007 22:08:36 -0000    1.49
--- doc/src/sgml/wal.sgml    11 Dec 2007 14:22:32 -0000
***************
*** 65,71 ****
     write caching.  On <productname>FreeBSD</> use
     <application>atacontrol</>.  (For SCSI disks use <ulink
     url="http://sg.torque.net/sg/sdparm.html"><application>sdparm</></ulink>
!    to turn off <literal>WCE</>.)  On <productname>Windows</> write caching is
     disabled by unchecking <literal>My Computer\Open\{select disk
     drive}\Properties\Hardware\Properties\Policies\Enable write caching on
     the disk</>.
--- 65,73 ----
     write caching.  On <productname>FreeBSD</> use
     <application>atacontrol</>.  (For SCSI disks use <ulink
     url="http://sg.torque.net/sg/sdparm.html"><application>sdparm</></ulink>
!    to turn off <literal>WCE</>.) On <productname>Solaris</> with UFS write cache
!    is disabled by default. Use <command>format -e</> to control it. ZFS works correctly
!    with enabled write cache. On <productname>Windows</> write caching is
     disabled by unchecking <literal>My Computer\Open\{select disk
     drive}\Properties\Hardware\Properties\Policies\Enable write caching on
     the disk</>.