[frr] changing address-family vpn&encap config

Hi all, this is related to cleaning up the confusion of treating the vpn safi as afi+safi, see https://github.com/freerangerouting/frr/issues/61. Does anyone object to the following change to *config* in *stable/2.0* - note this will break backwards compatibility (reading old will be preserved, but output will only be new) OLD address-family ipv4 address-family ipv4 (unicast|multicast) address-family ipv6 address-family ipv6 (unicast|multicast) address-family vpnv4 address-family vpnv4 unicast address-family vpnv6 address-family vpnv6 unicast address-family encap address-family encapv4 address-family encapv6 new address-family <ipv4|ipv6> [<unicast|multicast|vpn|encap>] //default is unicast Lou