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.
In nettle/md5.h, md5_init and md5_update are defined as macros to
nettle_md5_init and nettle_md5_update respectively. This causes
error when using MD5_params.md5_init and md5_update. This patch
renames these members as md5_init_func and md5_update_func to
avoid name conflict. For completeness, MD5_params.md5_final was
also renamed as md5_final_func.
The changes in curl_ntlm_core.c is conversion error and fixed by
casting to proper type.
