Implement key exchange messages and PMS derivation

This completes the first working version. No interop testing done yet.
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 2527a86..cac039a 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -2532,7 +2532,7 @@
             "$P_SRV debug_level=3 ecjpake_pw=bla" \
             "$P_CLI debug_level=3 ecjpake_pw=bla \
              force_ciphersuite=TLS-ECJPAKE-WITH-AES-128-CCM-8" \
-            1 \
+            0 \
             -c "add ciphersuite: c0ff" \
             -c "adding ecjpake_kkpp extension" \
             -s "found ecjpake kkpp extension" \