Merge branch 'evdns-tcp-pr-1004'

Merge branch 'evdns-tcp-pr-1004'

@seleznevae:

  "Added support for DNS requests via TCP. By default, requests are done
   via UDP. In case truncated response is received new attempt is done
   via TCP connection. Added 2 new macros DNS_QUERY_USEVC and
   DNS_QUERY_IGNTC to force all requests to be done via TCP and to disable
   switch to TCP in case of truncated responses.

   Also added possibility for DNS server to listen and receive requests on
   TCP port. Current implementation of TCP support in DNS server seems
   rather preliminary and maybe changes after discussion and code review.

   Fallback to TCP in case of truncated DNS requests is done automatically.
   To imitate the old behaviour macros DNS_QUERY_IGNTC should be used. To
   force all DNS requests to be done via TCP one should use the flag
   DNS_QUERY_USEVC. Names DNS_QUERY_IGNTC, DNS_QUERY_USEVC were chosen to
   imitate similar flags in c-ares and glibc."

Ok, interfaces looks good, merging to avoid stalling it for too long.

* evdns-tcp-pr-1004:
  evdns: fix coding style issues
  evdns: fix trailing whitespaces
  evdns: bufferevent_setcb before bufferevent_free is redundant
  evdns: Implement dns requests via tcp