set_seed(): range check the seed string

seed the SURF generator
filter ipv6 addrs out of root_hints if !ipv6

dot_sane(): simple dfa to verify the sanity of a dotted name

use cpython.bytes
use libc.errno

expose several socket methods to C/Cython/pxd

removed weird special-case code for linux: of course it has stdint [tested ubuntu 12.04 cython 0.18]