Re-added support for parsing and handling SSLv2 Client Hello messages

If the define POLARSSL_SSL_SRV_SUPPORT_SSLV2_CLIENT_HELLO is enabled,
the SSL Server module can handle the old SSLv2 Client Hello messages.

It has been updated to deny SSLv2 Client Hello messages during
renegotiation.

ChangeLog

diff --git a/ChangeLog b/ChangeLog
index f5d6b4a..e3611bd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -14,6 +14,8 @@
      PKCS#1 v2.1 functions
    * Added support for custom labels when using rsa_rsaes_oaep_encrypt()
      or rsa_rsaes_oaep_decrypt()
+   * Re-added handling for SSLv2 Client Hello when the define
+     POLARSSL_SSL_SRV_SUPPORT_SSLV2_CLIENT_HELLO is set
 
 Security
    * Removed further timing differences during SSL message decryption in