Updated version number to 2.4.2 for release

ChangeLog

@@ -1,8 +1,13 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
-= mbed TLS 2.x.x branch released xxxx-xx-xx
+= mbed TLS 2.4.2 branch released 2017-03-08
 
 Security
+   * Add checks to prevent signature forgeries for very large messages while
+     using RSA through the PK module in 64-bit systems. The issue was caused by
+     some data loss when casting a size_t to an unsigned int value in the
+     functions rsa_verify_wrap(), rsa_sign_wrap(), rsa_alt_sign_wrap() and
+     mbedtls_pk_sign(). Found by Jean-Philippe Aumasson.
    * Fixed potential livelock during the parsing of a CRL in PEM format in
      mbedtls_x509_crl_parse(). A string containing a CRL followed by trailing
      characters after the footer could result in the execution of an infinite