`i2d_RSAPublicKey` now supports (in OpenSSL 0.9.7 or later, so in all OpenSSL versions we support) allocating its own output buffer (using `OPENSSL_malloc`). Is this feature worth using in `crypto_pk_get_digest` (and some other functions which call `i2d_RSAPublicKey` twice to allocate a _temporary_ buffer)? (See the `i2d_X509(3ssl)` man page.)