Name resolution via TCP support

Supports _real_ name resolution via parent proxy over TCP in nserver /
dnspr.
Can be used to create UDP->TCP name proxy, e.g.

nserver 127.0.0.1/tcp
nscache 65535
auth none
dnspr
auth iponly
tcppm 53 77.88.8.8 53

now, all names are resolved via TCP connection to 77.88.8.8
(dns.yandex.ru).