Add correct flags for DTLS 1.2, update s_server and s_client to handle
DTLS 1.2 methods.

Currently no support for version negotiation: i.e. if client/server selects
DTLS 1.2 it is that or nothing.

Submitted by: Pierre Delaage

Don't verify our own responses.

Recognise verification arguments.

trusted store instead of the default which is to return an error if
we can't build the complete chain.

Just a sample, real world applications would have to be cleverer.

Add new verify options to set checks.

Remove previous -check* commands from s_client and s_server.

is needed to test some profiles/protocols which reject certificates
with unsupported versions.

Add support for separate verify and chain stores in s_client.