Revert "Remove heartbeats completely"

Done too soon, this is for future OpenSSL 1.2.0

This reverts commit 6c62f9e1639a7d1a879f363a99882920104dfedb.

Reviewed-by: Rich Salz <rsalz@openssl.org>
diff --git a/util/mkdef.pl b/util/mkdef.pl
index 3b8c5c4..c5884d3 100755
--- a/util/mkdef.pl
+++ b/util/mkdef.pl
@@ -101,7 +101,7 @@
 			 # RFC3779
 			 "RFC3779",
 			 # TLS
-			 "PSK", "SRP",
+			 "PSK", "SRP", "HEARTBEATS",
 			 # CMS
 			 "CMS",
                          "OCSP",