M2Crypto has been abandonded upstream, has many outstanding bugs,
and doesn't build unpatched on Fedora. Since the only thing M2Crypto
is being used for in the salt codebase is RSA support, using the PyCrypto
RSA module instead is pretty straight forward. Additionally, the RSA
module uses sign/verify terminology around our use of private encrypting
known tokens for verification purposes rather than private_encrypt and
public_descrypt, which makes reading the intent a little clearer.
