darwinssl: output cipher with text, remove SNI warning

The code was printing a warning when SNI was set up successfully. Oops.

Printing the cipher number in verbose mode was something only TLS/SSL
programmers might understand, so I had it print the name of the cipher,
just like in the OpenSSL code. That'll be at least a little bit easier
to understand. The SecureTransport API doesn't have a method of getting
a string from a cipher like OpenSSL does, so I had to generate the
strings manually.