(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.

  libcurl to resolve 'localhost' whatever name you use in the URL *if* you set
  the --interface option to (exactly) "LocalHost". This will enable us to
  write tests for custom hosts names but still use a local host server.

setup_once.h.  Inclusion of each header file is based on the definition of
NEED_MALLOC_H and NEED_MEMORY_H respectively.

which now also takes a protocol address family argument.

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.

  (http://curl.haxx.se/bug/view.cgi?id=1911069) that identified a race
  condition in the name resolver code when the DNS cache is shared between
  multiple easy handles, each running in simultaneous threads that could cause
  crashes.

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.

while () => while()
and some other minor re-indentings

libcurl. This also makes the options change name to --krb (from --krb4) and
CURLOPT_KRBLEVEL (from CURLOPT_KRB4LEVEL) but the old names are still

hash function for different hashes, and also expanded the default size for
the socket hash table used in multi handles to greatly enhance speed when
very many connections are added and the socket API is used.

since they're already included through "setup.h".