Handle read errors in Protocols.LysKOM.Raw.

If there is a network outage, con->read() will return 0 (not the empty
string) after a (long) while.  Treat that properly by calling
connection_lost() in that case as well.

Fixed a backrace in conwrite by returning 0 if the connection
is closed.
Testsuite: Preparations for testing TLS 1.3.

The SSL testsuite now knows some about which suites that are to be
obsoleted in TLS 1.3.