All uses changed. Remove the old SWAP.
Remove obvious comment about BLOCKSIZE.
(rol): New macro, moved here from md5.h.
(sha1_process_block): Remove an incoherent FIXME comment.
suffices with C89 or better.
(alignof): New macro, portable to all C89 hosts.
(UNALIGNED): Use it. Use uintptr_t if available, and assume
everything is unaligned otherwise; this is more portable than
assuming 'unsigned long int' will always work.