Logstash-forwarder requires Go-1.1/1.2

The SSL stuff in it doesn't work right with Go 1.3 yet.
1.2 doesn't have a derivation for darwin, so go 1.1 should work for
everyone
logstash_forwarder: specify platforms
libnftnl: Add derivation
docbook2x: Add platforms so that it builds on hydra
nftables: Add derivation