Properly cope with multiple configurations

Don't re-use an SSL context when a different cipher list (but the same
certificate/key file) is specified.
Merge pull request #8 from weiss/multiple-configs

Properly cope with multiple configurations
Always set (EC)DH parameters

Don't skip setting (EC)DH parameters when the first connection after
starting the server happens to be outgoing, because the OpenSSL context
will later be reused when accepting incoming connections.  This makes
sure that ephemeral (EC)DH cipher suites can be offered either way.
Merge pull request #9 from weiss/always-set-dh-params

Always set (EC)DH parameters