[ext/openssl] Allow encryption for PEM-encoding Elliptic Curve private keys
There has already been some #if 0-excluded code that would actually
take care of this, but it has not been implemented yet. The attached
patch allows to encrypt PEM-encoded private keys, Cipher and password
are ignored in the case of public keys (rather than raising an error).
The motivation for this patch is that it would provide uniform behavior
of all three public key systems supported in Ruby, RSA, DSA (who already
support PEM encryption) and now also Elliptic Curve. RDoc has been