Allow enabling of dummy error_strerror() to support some use-cases

Enable a dummy error function to make use of error_strerror() in
third party libraries easier.

Disable if you run into name conflicts and want to really remove the
error_strerror()

ChangeLog

diff --git a/ChangeLog b/ChangeLog
index 6339383..2689dd0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 PolarSSL ChangeLog
 
+= Development
+Changes
+   * Allow enabling of dummy error_strerror() to support some use-cases
+
 = Version 1.2.4 released 2013-01-25
 Changes
    * Added ssl_handshake_step() to allow single stepping the handshake process