researching it, it turned out he got a 550 response back from a SIZE command
  and then I fell over the text in RFC3659 that says:

   The presence of the 550 error response to a SIZE command MUST NOT be taken
   by the client as an indication that the file cannot be transferred in the
   current MODE and TYPE.

  In other words: the change I did on September 30th 2008 and that has been
  included in the last two releases were a regression and a bad idea. We MUST
  NOT take a 550 response from SIZE as a hint that the file doesn't exist.

  (http://curl.haxx.se/bug/view.cgi?id=2221237) that identified an infinite
  loop during GSS authentication given some specific conditions. With his
  patience and great feedback I managed to narrow down the problem and
  eventually fix it although I can't test any of this myself!

  (http://curl.haxx.se/bug/view.cgi?id=2351645) that identified a problem with
  the multi interface that occured if you removed an easy handle while in
  progress and the handle was used in a HTTP pipeline.

  bad fclose() after a fatal error had occured.
  (http://curl.haxx.se/bug/view.cgi?id=2382219)

  function when built to support SCP and SFTP that helps the library to know
  in which direction a particular libssh2 operation would return EAGAIN so
  that libcurl knows what socket conditions to wait for before trying the
  function call again. Previously (and still when using libssh2 0.18 or
  earlier), libcurl will busy-loop in this situation when the easy interface
  is used!

  used. It has been used since forever but it was never a good idea to use
  unless explicitly asked for.

  GSS/kerberos authentication (http://curl.haxx.se/bug/view.cgi?id=2284386)

  when uploading files to a single FTP server using multiple easy handle
  handles with the multi interface. Occasionally a handle would stall in
  mysterious ways.

  The problem turned out to be a side-effect of the ConnectionExists()
  function's eagerness to re-use a handle for HTTP pipelining so it would
  select it even if already being in use, due to an inadequate check for its
  chances of being used for pipelnining.

enabled and FTP disabled.

  (http://curl.haxx.se/bug/view.cgi?id=2255627) which pointed out that a
  program using libcurl's multi interface to download a HTTPS page with a
  libcurl built powered by OpenSSL, would easily get silly and instead hand
  over SSL details as data instead of the actual HTTP headers and body. This
  happened because libcurl would consider the connection handshake done too
  early. This problem was introduced at September 22nd 2008 with my fix of the
  bug #2107377

  The correct fix is now instead done within the GnuTLS-handling code, as both
  the OpenSSL and the NSS code already deal with this situation in similar
  fashion. I added test case 560 in an attempt to verify this fix, but
  unfortunately it didn't trigger it even before this fix!

Daniel Fandrich noticed that curl_addrinfo was also missing in the build
process of other four non-configure platforms. Added now.

system with a TEQL load-balancing device configured, which doesn't
have an address.  Thanks to Adam Sampson for spotting this (bug #2234923).

problem with MSVC 6 makefile that caused a build failure. It was noted that
the curl_addrinfo.obj reference was missing. I took the opportunity to sort
the list in which this was missing.

with ipv6-enabled c-ares

curl_easy_pause() during a chunky upload. Reported by Steve Roskowski.

  make CURLOPT_PROXYUSERPWD sort of deprecated. The primary motive for adding
  these new options is that they have no problems with the colon separator
  that the CURLOPT_PROXYUSERPWD option does.

  (http://curl.haxx.se/bug/view.cgi?id=2154627) which pointed out that libcurl
  uses strcasecmp() in multiple places where it causes failures when the
  Turkish locale is used. This is because 'i' and 'I' isn't the same letter so
  strcasecmp() on those letters are different in Turkish than in English (or
  just about all other languages). I thus introduced a totally new internal
  function in libcurl (called Curl_ascii_equal) for doing case insentive
  comparisons for english-(ascii?) style strings that thus will make "file"
  and "FILE" match even if the Turkish locale is selected.

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.

  fixed a CURLINFO_REDIRECT_URL memory leak and an additional wrong-doing:

  Any subsequent transfer with a redirect leaks memory, eventually crashing
  the process potentially.

  Any subsequent transfer WITHOUT a redirect causes the most recent redirect
  that DID occur on some previous transfer to still be reported.

  eventually identified a flaw in how the multi_socket interface in some cases
  missed to call the timeout callback when easy interfaces are removed and
  added within the same millisecond.

  curl_easy_setopt: CURLOPT_USERNAME and CURLOPT_PASSWORD that sort of
  deprecates the good old CURLOPT_USERPWD since they allow applications to set
  the user name and password independently and perhaps more importantly allow
  both to contain colon(s) which CURLOPT_USERPWD doesn't fully support.

  the app re-used the handle to do a connection to host B and then again
  re-used the handle to host A, it would not update the info with host A's IP
  address (due to the connection being re-used) but it would instead report
  the info from host B.

  gets a 550 response back for the cases where a download (or NOBODY) is
  wanted. It still allows a 550 as response if the SIZE is used as part of an
  upload process (like if resuming an upload is requested and the file isn't
  there before the upload). I also modified the FTP test server and a few test
  cases accordingly to match this modified behavior.

  libcurl to somewhat reduce the size of the binary. Run configure
  --disable-proxy.

  downloads!

  CURLINFO_REDIRECT_URL in multi mode" also contained a patch that fixed the
  problem.