Update to 5.81:

5.81  Mon Jan 14 05:17:08 MST 2013
- corrected load subroutine (SHA.pm) to prevent double-free
-- Bug #82655: Security issue - segfault
-- thanks to Victor Efimov and Nicholas Clark
for technical expertise and suggestions

5.80  Mon Dec 10 14:15:26 MST 2012
- obtained noticeable speedup on Intel/gcc
-- by setting -O1 and -fomit-frame-pointer
-- SHA-1 about 63% faster, SHA-2 improves 11-20%

5.74  Sat Nov 24 03:10:18 MST 2012
- handle wide-string input by converting to bytes first
-- viz. use SvPVbyte instead of SvPV in SHA.xs
-- thanks to Eric Brine for summary and code

5.73  Wed Oct 31 04:32:44 MST 2012
- provided workaround for DEC compiler bug (ref. Makefile.PL)

(wiz)