Added mechanism to provide alternative cipher / hash implementations

All symmetric cipher algorithms and hash algorithms now include support
for a POLARSSL_XXX_ALT flag that prevents the definition of the
algorithm context structure and all 'core' functions.

library/des.c

@@ -1,7 +1,7 @@
 /*
  *  FIPS-46-3 compliant Triple-DES implementation
  *
- *  Copyright (C) 2006-2010, Brainspark B.V.
+ *  Copyright (C) 2006-2013, Brainspark B.V.
  *
  *  This file is part of PolarSSL (http://www.polarssl.org)
  *  Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
@@ -35,6 +35,8 @@
 
 #include "polarssl/des.h"
 
+#if !defined(POLARSSL_DES_ALT)
+
 /*
  * 32-bit integer manipulation macros (big endian)
  */
@@ -751,6 +753,8 @@ int des3_crypt_cbc( des3_context *ctx,
     return( 0 );
 }
 
+#endif /* !POLARSSL_DES_ALT */
+
 #if defined(POLARSSL_SELF_TEST)
 
 #include <stdio.h>