doing an FTP transfer is removed from a multi handle before completion. The
  fix also fixed the "alive counter" to be correct on "premature removal" for
  all protocols.

detector.  Also changed tftp downloads to URL-unescape the downloaded
file name.

multi interface, but I could also repeat it doing multiple sequential ones
with the easy interface. Using Ciprian's test case, I could fix it.

cache within the multi handle.

command on subsequent requests on a re-used connection unless it has to.

Winsock and Cygwin need address family specification before bind(), this should be harmless for others.

from Curl_client_write

Fixed handling of retransmitted blocks on transmit
Properly aligned data to transmit within packet
Replaced calls to strerror() with Curl_strerror()

thus works reliably on more platforms.

(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.

called bind() with a too big argument in the 3rd parameter and at least
Tru64, AIX and IRIX seem to be very picky about it.

512 bytes could have random garbage appended.  Also, stop processing TFTP
packets which are too short to be legal.

issues in the code.

that's in <winsock2.h>. Hence tftp.c wouldn't compile on WinCE.

struct instead to use.

in files that actually need the struct.

Should we do this for all targets?

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