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.

In this change, --metalink option no longer takes argument.  If
it is specified, given URIs are processed as Metalink XML file.
If given URIs are remote (e.g., http URI), curl downloads it
first. Regardless URI is local file (e.g., file URI scheme) or
remote, Metalink XML file is not written to local file system and
the received data is fed into Metalink XML parser directly.  This
means with --metalink option, filename related options like -O
and -o are ignored.

Usage examples:

$ curl --metalink http://example.org/foo.metalink

This will download foo.metalink and parse it and then download
the URI described there.

$ curl --metalink file://foo.metalink

This will parse local file foo.metalink and then download the URI
described there.

When creating metalink_checksum from metalink_checksum_t, first
check hex digest is valid for the given hash function.  We do
this check in the order of digest_aliases so that first good
match will be chosen (strongest hash function available).  As a
result, the metalinkfile now only contains at most one
metalink_checksum because other entries are just redundant.

http://curl.haxx.se/mail/archive-2012-06/0028.html

Removed two, not intended to exist, RESOURCE declarations.

Bug: http://curl.haxx.se/bug/view.cgi?id=3535977

And sorted configuration hunks to reflect same internal order
as the one shown in the usage message.

Increase decrypted and encrypted cache buffers using limitted
doubling strategy. More information on the mailinglist:
http://curl.haxx.se/mail/lib-2012-06/0255.html

It updates the two remaining reallocations that have already been there
and fixes the other one to use the same "do we need to increase the
buffer"-condition as the other two.  CURL_SCHANNEL_BUFFER_STEP_SIZE was
renamed to CURL_SCHANNEL_BUFFER_FREE_SIZE since that is actually what it
is now.  Since we don't know how much more data we are going to read
during the handshake, CURL_SCHANNEL_BUFFER_FREE_SIZE is used as the
minimum free space required in the buffer for the next operation.
CURL_SCHANNEL_BUFFER_STEP_SIZE was used for that before, too, but since
we don't have a step size now, the define was renamed.

In schannel_connect_step2() doread should be initialized based
on connssl->connecting_state.

Test definition section parts which needed to include xml-lingo as contents
of that part required that the xml-blurb was written as a single line. Now the
xml-data inside the part can be written multiline making it more readable.

Tested with <client><file> part which is written to disk before <command> runs.