Added md_process() to MD layer for generic internal access to hash
process functions

Access to process functions is needed to reduce possible timing attacks
on SSL MAC checks. As SSL is set to move to using the dynamic MD layer,
the MD layer needs access to these process functions as well.
diff --git a/include/polarssl/sha4.h b/include/polarssl/sha4.h
index 6aae124..5563676 100644
--- a/include/polarssl/sha4.h
+++ b/include/polarssl/sha4.h
@@ -161,6 +161,9 @@
  */
 int sha4_self_test( int verbose );
 
+/* Internal use */
+void sha4_process( sha4_context *ctx, const unsigned char data[128] );
+
 #ifdef __cplusplus
 }
 #endif