cbc-over-mbuf functions in sys/crypto.
the change should make it much easier to switch crypto function to
machine-dependent ones (like assembly code under sys/arch/i386/crypto?).
also it should be much easier to import AES algorithms.
XXX: it looks that past blowfish-cbc code was buggy. i ran some test pattern,
and new blowfish-cbc code looks more correct. there's no interoperability
between the old code (before the commit) and the new code (after the commit).
XXX: need serious interop tests before move it into 1.5 branch
bb8d535cc5