ext/digest/sha2/sha2.c (SHA256_Update, SHA512_Update): avoid Bus
Error caused by unalignment access on Sparc-Solaris (and possibly on
other similar environment.) This patch just do memcpy always instead
of checking architecture. I see no perf drop on my 64bit env. For
more details, see #4320.
test/digest/test_digest.rb: add test for unalignment access.