Release Notes: A bug that prevented building M2Crypto when OpenSSL was built without EC support was fixed. This was the case on Fedora Core at least. Upgrading from 0.19 is not needed if you were able to build previously.
Release Notes: typedef Py_ssize_t was insufficiently guarded, and now follows PEP 353. This prevented building on at least Red Hat Linux and Debian Linux (unstable).