Adapted from BoringSSL. Added a test.

The extension parsing code is already attempting to already handle this for
some individual extensions, but it is doing so inconsistently. Duplicate
efforts in individual extension parsing will be cleaned up in a follow-up.
Reviewed-by: NStephen Henson <steve@openssl.org>

Add function to delete extensions and fix ClientHello repacking.
Reviewed-by: NMatt Caswell <matt@openssl.org>

Reviewed-by: NMatt Caswell <matt@openssl.org>

Add ServerHello parsing to TLSProxy.
Also add some (very) limited ServerKeyExchange parsing.
Add the capability to set client and server cipher lists
Fix a bug with fragment lengths
Reviewed-by: NRichard Levitte <levitte@openssl.org>

This commit provides a set of perl modules that support the testing of
libssl. The test harness operates as a man-in-the-middle proxy between
s_server and s_client. Both s_server and s_client must be started using the
"-testmode" option which loads the new OSSLTEST engine.

The test harness enables scripts to be written that can examine the packets
sent during a handshake, as well as (potentially) modifying them so that
otherwise illegal handshake messages can be sent.
Reviewed-by: NRichard Levitte <levitte@openssl.org>