start reducing the attack surface of lynx.

leave gopher, news, and dired in place for now. but we will soon catch up
to the security level of internet explorer 7 by removing these too.

ok's for the version of this diff that removes even more protocols from
deraadt@, tedu@. general support from other devs.
Add some services needed by comms/hylafax
ok ajacoutot@
Verify the checksum of the echo reply fragment based on the echo
request.
Don't write out a new resolv.conf until the new address is added
and we become responsible for the interface. Don't write out a new
resolv.conf when our address has been deleted and we are no longer
responsible for the interface. Less writing is more better.