Cleaner TLS/SSL session resumption prevention.

This approach removes only the SessionTickets extension instead of
removing all TLS extensions. Moreover, it does this by modifying the
ClientHello instead of the ServerHello. This is advantageous because
this makes both the client and the server perform a full handshake.
Merge pull request #47 from google/cleaner-resumption-prevention

Cleaner TLS/SSL session resumption prevention.