Fix for strict aliasing rules.
* cipher/rijndael.c (do_setkey, prepare_decryption): Use u32_a_t for casting.
gcc 4.7.1 now show warnings for more functions. Like:
rijndael.c:412:19: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
This fixes them using the may_alias attribute.