Note: This is included in OpenSSL since 1.0.1d (I think).
This patch is for OpenSSL's capi engine. It adds support for private keys
inside a machine keystore (MACHINE_KEYSET). It has been tested with
OpenSSL version 1.0.1 but since it is very simple it should work with most
future versions of this engine (until they maybe finally implement it by
themselves.