Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Make test00 compilable again.

Add a testcase which validates that the same buffer can be passed to
rijndael_blockDecrypt() as both input and output.

This property is important because inside rijndael we can get away
with allocating just a 16 byte "work" buffer on the stack (which
is very cheap), whereas the calling code would need to allocate the
full sized buffer, and in all likelyhood would have to do so with
an expensive malloc(9).