Print "parsing (...) OK" only when no warnings are generated.  If
no file is found in Metalink, treat it FAILED.

If no digest is provided, print WARNING in parse_metalink().
Also print validating FAILED after download.

These changes make tests 2012 to 2016 pass.

Reported by Tatsuhiro Tsujikawa

http://curl.haxx.se/mail/lib-2012-06/0371.html

Allow NTLM authentication when building using SecureTransport (Darwin) for SSL.

This uses CommonCrypto, a cryptography library that ships with all versions of
iOS and Mac OS X. It's like OpenSSL's libcrypto, except that it's missing a few
less-common cyphers and doesn't have a big number data structure.

Before commit 2dded8fe (dec 2010) there was logic that used
RAND_screen() at times and now I remove the leftover #ifdef check for
it.

The seeding code that uses Curl_FormBoundary() in ossl_seed() is dubious
to keep since it hardly increases randomness but I fear I'll break
something if I remove it now...

- Renamed st_ function prefix to darwinssl_
- Renamed Curl_st_ function prefix to Curl_darwinssl_
- Moved the duplicated ssl_connect_done out of the #ifdef in lib/urldata.h
- Fixed a teensy little bug that made non-blocking connection attempts block
- Made it so that it builds cleanly against the iOS 5.1 SDK

Fixed warning: dereferencing pointer does break strict-aliasing rules
by using a union inside the struct Curl_sockaddr_storage declaration.

curl_ntlm_msgs.c would previously use an #ifdef maze and direct
SSL-library calls instead of using the SSL layer we have for this
purpose.

Documented that --include will be ignored if both --metalink
and --include are specified.
Also documented that a Metalink file in the local file system
cannot be used if FILE protocol is disabled.

Bug: http://curl.haxx.se/mail/lib-2012-06/0302.html
Reported by: Nagai H

Bug: http://curl.haxx.se/mail/lib-2012-06/0094.html
Reported by: Dan

Including headers in response body will break Metalink XML parser.
If it is included in the file described in Metalink XML, hash check
will fail. Therefore, --include should be ignored if --metalink is
used.

The noprogress and isatty in Configurable are global, in a sense
that they persist in one curl invocation. Currently once one
download writes its response data to tty, they are set to FALSE
and they are not restored on successive downloads.  This change
first backups the current noprogress and isatty, and restores
them when download does not write its data to tty.