Fix handling of long PSK identities

backport from c3b5d83

see #238
diff --git a/ChangeLog b/ChangeLog
index 5d505b5..89a89f8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -12,6 +12,9 @@
    * Fix unused function warning when using MBEDTLS_MDx_ALT or
      MBEDTLS_SHAxxx_ALT (found by Henrik) (#239)
    * Fix memory corruption in pkey programs (found by yankuncheng) (#210)
+   * Fix memory corruption on client with overlong PSK identity, around
+     SSL_MAX_CONTENT_LEN or higher - not triggerrable remotely (found by
+     Aleksandrs Saveljevs) (#238)
 
 = mbed TLS 1.3.12 released 2015-08-11