Use protocol-relative link to specific email, and switch to using
permanant link to it.
Simplify four manpage links to remove unnecessary parameters, and link
to the most default version of each man page rather than hard-coding the
version from 6.0.  The pae(4) man page is only available on i386, so that
needs to be stated explicitly.

Use &cgibase; rather than hardcoding http://www.freebsd.org/cgi/
Use &cgibase; rather than hardcoding http://www.freebsd.org/cgi/

There are a few remaining explicit uses of http://www.freebsd.org/cgi/
but all of these appear to be outdated e.g. pointing to GNATS) and need
updating.

Switch &cgibase; to use protocol-relative links, rather than hardcoding
http.  Switch two others (ftpbase and ftpbaseerrata) whilst here.