Add AEAD as a "MAC alias" so that it is possible to identify/select ciphers

Add AEAD as a "MAC alias" so that it is possible to identify/select ciphers
that use AEAD instead of a MAC. This allows for TLSv1.2 AEAD ciphers
(effectively the only ciphers that are still considered to be secure) to be
selected using TLSv1.2+AEAD as a cipher string.

ok bcook@ doug@ miod@