Use proper PEM_read_bio_RSA_PUBKEY

Using the other results in: error reading public key: error:0906D06C:PEM routines:PEM_read_bio:no start line

Also see:
http://stackoverflow.com/questions/7818117/why-i-cant-read-openssl-generated-rsa-pub-key-with-pem-read-rsapublickey