openssl: disable digests by default, misc fixes

openssl: disable digests by default, misc fixes

Openssh uses digest contexts across forks, which is not supported by the
/dev/crypto engine.  The speed of digests is usually not worth enabling
them anyway.  This changes the default of the DIGESTS option to NONE, so
the user still has the option to enable them.

Added another patch related to the use of encryption contexts across
forks, that ignores a failure to close a previous open session when
reinitializing a context, instead of failing the reinitialization.

Added a link to the Cryptographic Hardware Accelerators document to the
engine pacakges description, to provide more detailed instructions to
configure the engines.

Revert the removal of the OPENSSL_ENGINE_CRYPTO symbol, currently used
by openssh.  There is an open PR to update openssh; when merged, this
symbol can be safely removed.

Signed-off-by: Eneas U de Queiroz <cote2004-github@yahoo.com>
Signed-off-by: Hans Dedecker <dedeckeh@gmail.com> [refresh patches]