sslutil: calculate host fingerprints from additional algorithms Currently, we only support defining host fingerprints with SHA-1. A future patch will introduce support for defining fingerprints using other hashing algorithms. In preparation for that, we rewrite the fingerprint verification code to support multiple fingerprints, namely SHA-256 and SHA-512 fingerprints. We still only display the SHA-1 fingerprint. We'll have to revisit this code once we support defining fingerprints with other hash functions. As part of this, I snuck in a change to use range() instead of xrange() because xrange() isn't necessary for such small values.

util: add sha256 Upcoming patches will teach host fingerprint checking to verify non-SHA1 fingerprints. Many x509 certificates these days are SHA-256. And modern browsers often display the SHA-256 fingerprint for certificates. Since SHA-256 fingerprints are highly visible and easy to obtain, we want to support them for fingerprint pinning. So add SHA-256 support to util. I did not add SHA-256 to DIGESTS and DIGESTS_BY_STRENGTH because this will advertise the algorithm on the wire protocol. I wasn't sure if that would be appropriate. I'm playing it safe by leaving it out for now.

sslutil: move CA file processing into _hostsettings() The CA file processing code has been moved from _determinecertoptions into _hostsettings(). As part of the move, the logic has been changed slightly and the "cacerts" variable has been renamed to "cafile" to match the argument used by SSLContext.load_verify_locations(). Since _determinecertoptions() no longer contains any meaningful code, it has been removed.