select() overhaul fix.

#1098843. In short, a shared DNS cache was setup for a multi handle and when
the shared cache was deleted before the individual easy handles, the latter
cleanups caused read/writes to already freed memory.

a precedence problem with the zlib header. See CHANGES for details.

ssluse.*: Added SSL_strerror(). Curl_SSL_engines_list() now returns a slist
which must be freed by caller.

UrlState sub-struct. Also made the engine_list exist for non-ssl builds to
make curl build.

Added Curl_SSL_engines_list(), cleanup SSL in url.c
(no HAVE_OPENSSL_x etc.).

clash with djgpp ioctl() macro in setup.h.

If EPSV, EPRT or LPRT is tried and doesn't work, it will not be retried on
the same server again even if a following request is made using a persistent
connection.

If a second request is made to a server, requesting a file from the same
directory as the previous request operated on, libcurl will no longer make
that long series of CWD commands just to end up on the same spot. Note that
this is only for *exactly* the same dir. There is still room for improvements
to optimize the CWD-sending when the dirs are only slightly different.

Added test 210, 211 and 212 to verify these changes. Had to improve the
test script too and added a new primitive to the test file format.

  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.

  replacement, curl only replaced the Host: header on the initial request
  and didn't replace it on the following ones. This resulted in requests with
  two Host: headers.

  Now, curl checks if the location is on the same host as the initial request
  and then continues to replace the Host: header. And when it moves to another
  host, it doesn't replace the Host: header but it also doesn't make the
  second Host: header get used in the request.

  This change is verified by the two new test cases 184 and 185.

implicitly converting it to int

linked list for name resolved data, even on hosts/systems with only IPv4
stacks as this simplifies a lot of code.

enough. This is most likely the bug Jean-Louis Lemaire reported that makes
2GB FTP uploads to report error when completed.
Also padded comments to get them aligned again, only for visibility.

server doesn't require any auth at all and then we just continue nicely. We
now have an extra bit in the connection struct named 'authprobe' that is TRUE
when doing pure "HTTP authentication probing".

if a connection is tunneled through a proxy. A tunnel is done with CONNECT,
either when using HTTPS or FTPS, or if explicitly enabled by the app.

not be used both in one request. Fixed it and added test case 172 to verify.

take a CURLcode as a second argument, that is non-zero when Curl_done()
is called after an error was returned from Curl_do() (or similar).

Also, make sure we have room for the trailing zero, only scan to size-1.

Gisle Vanem reported.

all things up to work with encoded host names internally, as well as keeping
'display names' to show in debug messages. IDN resolves work for me now using
ipv6, ipv4 and ares resolving. Even cookies on IDN sites seem to do right.

usage.

  stuff added a few weeks ago.  Turns out that if you specify --proxy-ntlm and
  communicate with a proxy that requires basic authentication, the proxy
  properly returns a 407, but the failure detection code doesn't realize it
  should give up, so curl returns with exit code 0. Test case 162 verifies
  this.

160 shows.

We got no data and we attempted to re-use a connection. This might happen if
the connection was left alive when we were done using it before, but that was
closed when we wanted to read from it again. Bad luck. Retry the same request
on a fresh connect!

Deleted the sockerror variable again, it serves no purpose anymore.

length limit of the hostname part of the URL.