OS X shared memory documentation

I finally figured out what the issue was with OS X blowing away shared
memory settings  from /etc/sysctl.conf. I added a note to the 8.1 docs
already, and here's a patch against -HEAD.
--
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461