Fix compiler warning: conditional expression is constant

fix printf-style format strings

  interval even during very slow connects.

  (http://curl.haxx.se/bug/view.cgi?id=2870221) that libcurl returned an
  incorrect return code from the internal trynextip() function which caused
  him grief. This is a regression that was introduced in 7.19.1 and I find it
  strange it hasn't hit us harder, but I won't persue into figuring out
  exactly why.

  SO_SNDBUF to CURL_WRITE_SIZE even if the SO_SNDBUF starts out larger.  The
  patch doesn't do a setsockopt if SO_SNDBUF is already greater than
  CURL_WRITE_SIZE. This should help folks who have set up their computer with
  large send buffers.

  setting a file descriptor non-blocking. Used by the functionality Eric
  himself brough on June 15th.

  well. See change 28 Apr 2009.

  (http://curl.haxx.se/bug/view.cgi?id=2783090) pointing out that on windows
  we need to grow the SO_SNDBUF buffer somewhat to get really good upload
  speeds. http://support.microsoft.com/kb/823764 has the details. Friends
  confirmed that simply adding 32 to CURL_MAX_WRITE_SIZE is enough.

  CURLOPT_LOCALPORT were used together (the local port bind failed), and
  Markus Koetter provided the fix!

changed HAVE_SIN6_SCOPE_ID define to HAVE_SOCKADDR_IN6_SIN6_SCOPE_ID since just found that ares already uses this define.

fix compilation on Cell (reported by Jeff Curley).

non-blocking mode, and decouple function detection from function capability.

which now also takes a protocol address family argument.

  problem with my CURLINFO_PRIMARY_IP fix from October 7th that caused a NULL
  pointer read. I also took the opportunity to clean up this logic (storing of
  the connection's IP address) somewhat as we had it stored in two different
  places and ways previously and they are now unified.

and isn't strictly needed here.

And on the other hand a message after setsockopt() certainly must use SOCKERRNO.

systems supporting getifaddrs(). Also fixed a problem where an IPv6
address could be chosen instead of an IPv4 one for --interface when it
involved a name lookup.

1021 and 1067.

  parser to allow numerical IPv6-addresses to be specified with the scope
  given, as per RFC4007 - with a percent letter that itself needs to be URL
  escaped. For example, for an address of fe80::1234%1 the HTTP URL is:
  "http://[fe80::1234%251]/"

an IPv6 address.

  curl_easy_getinfo. It returns a pointer to a string with the most recently
  used IP address. Modified test case 500 to also verify this feature. The
  implementing of this feature was sponsored by Lenny Rachitsky at NeuStar.

  and receive data over a connection previously setup with curl_easy_perform()
  and its CURLOPT_CONNECT_ONLY option. The sendrecv.c example was added to
  show how they can be used.

  since libcurl used getprotobyname() and that isn't thread-safe. We now
  switched to use IPPROTO_TCP unconditionally, but perhaps the proper fix is
  to detect the thread-safe version of the function and use that.
  http://curl.haxx.se/mail/lib-2008-05/0011.html

  uses the CURLOPT_OPENSOCKETFUNCTION callback to create a unix domain socket
  to a http server.