from hostip.h to setup.h in order to allow proper inclusion in any file.

This represents no functional change at all in which resolver is used,
everything still works as usual, internally and externally there is no
difference in behavior.

removal of Curl_addrinfo_copy(), Curl_addrinfo6_callback(), and
Curl_addrinfo4_callback()

  (http://curl.haxx.se/bug/view.cgi?id=2891595) which identified how an entry
  in the DNS cache would linger too long if the request that added it was in
  use that long. He also provided the patch that now makes libcurl capable of
  still doing a request while the DNS hash entry may get timed out.

which now also takes a protocol address family argument.

implementation from lib/hostip6.c to lib/curl_addrinfo.c
and prototypes from lib/hostip.h to lib/curl_addrinfo.h

Use a wrapper function to call system's getaddrinfo().

Curl_resolv_timeout function to reduce coupling.

  edited it slightly. Now you should be able to use IPv6 addresses fine even
  with libcurl built to use c-ares.

The signalling of that a global DNS cache is wanted is done by setting the
option but the setting of the internal variable that it is in use must not be
done until it finally actually gets used!

NOTE and WARNING: I noticed that you can't actually switch off the global dns
cache with CURLOPT_DNS_USE_GLOBAL_CACHE but you couldn't do that previously
either and the option is very clearly and loudly documented as DO NOTE USE so
I won't bother to fix this bug now.

silly code left from when we switched to let the multi handle "hold" the dns
cache when using the multi interface... Of course this only triggered when a
certain function call returned error at the correct moment.

notifier callback(s).

sent by Dmitry Mityugov.

cache within the multi handle.

code rearrange to fit the future better.

(http://curl.haxx.se/bug/view.cgi?id=1431750) helped me identify and fix two
different but related bugs:

1) Removing an easy handle from a multi handle before the transfer is done
   could leave a connection in the connection cache for that handle that is
   in a state that isn't suitable for re-use. A subsequent re-use could then
   read from a NULL pointer and segfault.

2) When an easy handle was removed from the multi handle, there could be an
   outstanding c-ares DNS name resolve request. When the response arrived,
   it caused havoc since the connection struct it "belonged" to could've
   been freed already.

Now Curl_done() is called when an easy handle is removed from a multi handle
pre-maturely (that is, before the transfer was complteted). Curl_done() also
makes sure to cancel all (if any) outstanding c-ares requests.

Fix compiler warning and compatibility issue with the type of the parameter used in getnameinfo() to receive the length of the sockaddr struct.

from url.c: Curl_disconnect().

The tag 'before_ftp_statemachine' was set just before this commit in case
of future need.

CURLE_OK or CURLE_OUT_OF_MEMORY.
Add typecast in hostares.c.

of typecasts all over

linked list for name resolved data, even on hosts/systems with only IPv4
stacks as this simplifies a lot of code.