text from OpenSSL.

with the multi interface and multi-part formposts. The fix from February
22nd could make the Curl_done() function get called twice on the same
connection and it was not designed for that and thus tried to call free() on
an already freed memory area!

is used properly.

callback" error message so I've now made the setting of that callback not be
as critical as before. The function is only used for additional loggging/
trace anyway so a failure just means slightly less data. It should still be
able to proceed and connect fine to the server.

accordingly.

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

(http://curl.haxx.se/bug/view.cgi?id=1431750) helped me identify and fix two
different but related bugs:

1) Removing an easy handle from a multi handle before the transfer is done
   could leave a connection in the connection cache for that handle that is
   in a state that isn't suitable for re-use. A subsequent re-use could then
   read from a NULL pointer and segfault.

2) When an easy handle was removed from the multi handle, there could be an
   outstanding c-ares DNS name resolve request. When the response arrived,
   it caused havoc since the connection struct it "belonged" to could've
   been freed already.

Now Curl_done() is called when an easy handle is removed from a multi handle
pre-maturely (that is, before the transfer was complteted). Curl_done() also
makes sure to cancel all (if any) outstanding c-ares requests.

type to the already provided type CURLPROXY_SOCKS4.
I added a --socks4 option that works like the current --socks5 option but
instead use the socks4 protocol.