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.