Free an existing domain before replacing it.

Bug: https://github.com/curl/curl/issues/635


Reported-by:  <silveja1@users.noreply.github.com>

Closes #632

I removed the scheme prefix from the URLs references this host name, as
we don't own/run that anymore but the name is kept for historic reasons.

It isn't used by the code in current conditions but for safety it seems
sensible to at least not crash on such input.

Extended unit test 1395 to verify this too as well as a plain "/" input.

Closes #621

Due to path separators being incorrectly sanitized in --output
pathnames, eg -o c:\foo => c__foo

This is a partial revert of 3017d8a8 until I write a proper fix. The
remote-name will continue to be sanitized, but if the user specified an
--output with string replacement (#1, #2, etc) that data is unsanitized
until I finish a fix.

Bug: https://github.com/bagder/curl/issues/624
Reported-by: Octavio Schroeder

.. also warn about letting the server pick the filename.

Closes #617

Closes https://github.com/bagder/curl/pull/618

tool_doswin.c:185:14: warning: 'msdosify' defined but not used
[-Wunused-function]

Closes https://github.com/bagder/curl/pull/616

Reported-by: Bernard Spil

Proxy NTLM authentication should compare credentials when
re-using a connection similar to host authentication, as it
authenticate the connection.

Example:
curl -v -x http://proxy:port http://host/ -U good_user:good_pwd
  --proxy-ntlm --next -x http://proxy:port http://host/
    [-U fake_user:fake_pwd --proxy-ntlm]

CVE-2016-0755

Bug: http://curl.haxx.se/docs/adv_20160127A.html

curl does not sanitize colons in a remote file name that is used as the
local file name. This may lead to a vulnerability on systems where the
colon is a special path character. Currently Windows/DOS is the only OS
where this vulnerability applies.

CVE-2016-0754

Bug: http://curl.haxx.se/docs/adv_20160127B.html

Current FAQ didn't make it clear where the main repo is.

Closes #612

bug: http://curl.haxx.se/mail/lib-2016-01/0123.html

- Switch from verifying a pinned public key in a callback during the
certificate verification to inline after the certificate verification.

The callback method had three problems:

1. If a pinned public key didn't match, CURLE_SSL_PINNEDPUBKEYNOTMATCH
was not returned.

2. If peer certificate verification was disabled the pinned key
verification did not take place as it should.

3. (related to #2) If there was no certificate of depth 0 the callback
would not have checked the pinned public key.

Though all those problems could have been fixed it would have made the
code more complex. Instead we now verify inline after the certificate
verification in mbedtls_connect_step2.

Ref: http://curl.haxx.se/mail/lib-2016-01/0047.html
Ref: https://github.com/bagder/curl/pull/601

Because disabling the peer verification (--insecure) must not disable
the public key pinning check (--pinnedpubkey).

The CURLOPT_SSH_PUBLIC_KEYFILE option has been documented to handle
empty strings specially since curl-7_25_0-31-g05a443a but the behavior
was unintentionally removed in curl-7_38_0-47-gfa7d04f.

This commit restores the original behavior and clarifies it in the
documentation that NULL and "" have both the same meaning when passed
to CURLOPT_SSH_PUBLIC_KEYFILE.

Bug: http://curl.haxx.se/mail/lib-2016-01/0072.html

... by extracting the LIB + REASON from the OpenSSL error code. OpenSSL
1.1.0+ returned a new func number of another cerfificate fail so this
required a fix and this is the better way to catch this error anyway.

The configure test uses AC_TRY_RUN to figure out if an ipv6 socket
works, and testing like that doesn't work for cross-compiles. These days
IPv6 support is widespread so a blind guess is probably more likely to
be 'yes' than 'no' now.

Further: anyone who cross-compiles can use configure's --disable-ipv6 to
explicitly disable IPv6 and that also works for cross-compiles.

Made happen after discussions in issue #594