SHA clean-up and (LP64) tune-up.

"Clean-up" stands for the fact that it's using common message digest
template ../md32_common.h and sha[1_]dgst.c are reduced down to
'#define SHA_[01]' and then '#include "sha_locl.h"'. It stands "(LP64)"
there because it's 64 bit platforms which benefit most from the tune-up.
The updated code exhibits 40% performance improvement on IRIX64
(sounds too good, huh? I probably should double check if it's not
some cache trashing that was holding it back before), 28% - on
Alpha Linux and 12% - Solaris 7/64.