doc/go1.3.html: explain the change to the memory model
doc/go1.3.html: explain the change to the memory model

LGTM=iant, rsc
R=rsc, iant, mtj
CC=golang-codereviews
https://codereview.appspot.com/80260044

webfd/go-zh,sanjosh/sanjos100-tipc,rdp/rogerpack2005-golang,rdp/rogerpack2005-golang,rdp/rogerpack2005-golang,sanjosh/sanjos100-tipc,bryanxu/go-zh,d0f/go-zh,rdp/rogerpack2005-golang,d0f/go-zh,d0f/go-zh,d0f/go-zh,rdp/rogerpack2005-golang,webfd/go-zh,webfd/go-zh,webfd/go-zh,webfd/go-zh,sanjosh/sanjos100-tipc,bryanxu/go-zh,bryanxu/go-zh,bryanxu/go-zh,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,bryanxu/go-zh,webfd/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,d0f/go-zh,bryanxu/go-zh,sanjosh/sanjos100-tipc,rdp/rogerpack2005-golang,bryanxu/go-zh,bryanxu/go-zh,rdp/rogerpack2005-golang,webfd/go-zh,rdp/rogerpack2005-golang,d0f/go-zh,d0f/go-zh,webfd/go-zh