allow applications to set their own socket options.

(http://curl.haxx.se/bug/view.cgi?id=1481217), with follow-ups by Michele Bini
and David Byron. libcurl previously wrongly used GetLastError() on windows to
get error details after socket-related function calls, when it really should
use WSAGetLastError() instead.

When changing to this, the former function Curl_ourerrno() is now instead
called Curl_sockerrno() as it is necessary to only use it to get errno from
socket-related functions as otherwise it won't work as intended on Windows.

one

code rearrange to fit the future better.

(sorry, I don't know how to add this to the configure process).

(occurs w/o ENABLE_IPV6).

curl tool with --local-port. Plain and simply set the range of ports to bind
the local end of connections to. Implemented on to popular demand.

Not extensively tested. Please let me know how it works.

windows.h winsock.h winsock2.h ws2tcpip.h is done in setup.h

bug #1326306

protocol sockets even if the resolved address may say otherwise

added. TODO: add them to docs. add TFTP server to test suite. add TFTP to
list of protocols whereever those are mentioned.

mode. (djgpp/Watt-32 has 3 ways). Should rewrite this using
"#elif ..", but maybe there is still broken cpp around?

we should make it do that...)

VS2005.

Bug report #1124588 by David

timed out" even though the reason was different. Fixed this problem by not
setting this timeout to zero when using multi.

Needed elsewhere too?

the multi interface

  app to retrieve the errno variable after a (connect) failure. It will make
  sense to provide this for more failures in a more generic way, but let's
  start like this.