Implementation of a generic wrap interface for bignum and diffie-hellman
based upon Damien's wrap code in openssh-openbsd. This commit adds the
generic interface along with the backing code for openssl, cng, and cng
with an openssl fallback. Currently, openssl is the only provider for
bignum and the diffie-hellman generic interface is only for static and
negotiated oakley groups..
dkulwin