[FIX] Adds better keyserver support with tls (via gnutls) capable curl [#144 state:fixed]

- Adds gnutls and all its dependencies.
  gnutls will be able to lookup root CAs from the keychain with the help of a patch from VLC
- Adds curl with gnutls support instead of OS X's openssl which doesn't support tls1.x
  Removes the old curl version.
- Adds Homebrew helpers to build a universal library for Formulas that can't do that natively. (e.g. nettle, gmp)