Added do { ... } while (0) around block macros.

Added do { ... } while (0) around block macros.
(serpent_key_t): Deleted array typedef.
(ROL32, ROR32): Renamed macros, were rol and ror.
(KS_RECURRENCE, KS): New macros.
(serpent_key_pad): Renamed, from...
(serpent_key_prepare): ...old name.
(serpent_subkeys_generate): Deleted function.
(serpent_set_key): Rewrote the generation of subkeys. Reduced both
temporary storage and code size (less unrolling)

Rev: nettle/ChangeLog:1.173
Rev: nettle/serpent.c:1.6