Update the i386 platform page to closer reflect the early 21st century.
Gently push people towards the amd64 platform, especially for machines
with >4GiB RAM.  Drop one dead link, and one link to a very outdated page.


git-svn-id: svn+ssh://svn.freebsd.org/doc/head@45547 c2e8774f-c49f-e111-b436-862b2bbc8956