Renamed error_strerror() to the less conflicting polarssl_strerror()

Ability to keep old function error_strerror() as well with
POLARSSL_ERROR_STRERROR_BC. Also works with
POLARSSL_ERROR_STRERROR_DUMMY.

include/polarssl/config.h

@@ -325,6 +325,17 @@
  */
 #define POLARSSL_KEY_EXCHANGE_ECDHE_RSA_ENABLED
 
+/**
+ * \def POLARSSL_ERROR_STRERROR_BC
+ *
+ * Make available the backward compatible error_strerror() next to the
+ * current polarssl_strerror().
+ *
+ * Disable if you run into name conflicts and want to really remove the
+ * error_strerror()
+ */
+#define POLARSSL_ERROR_STRERROR_BC
+
 /**
  * \def POLARSSL_ERROR_STRERROR_DUMMY
  *

include/polarssl/error.h

@@ -103,7 +103,11 @@ extern "C" {
  * \param buffer    buffer to place representation in
  * \param buflen    length of the buffer
  */
+void polarssl_strerror( int errnum, char *buffer, size_t buflen );
+
+#if defined(POLARSSL_ERROR_STRERROR_BC)
 void error_strerror( int errnum, char *buffer, size_t buflen );
+#endif
 
 #ifdef __cplusplus
 }