This is yet another patch to _ssl.c that sets the
underlying BIO to non-blocking if the socket being
wrapped is non-blocking.  It also correctly loops when
SSL_connect, SSL_write, or SSL_read indicates that it
needs to read or write more bytes.

This seems to fix bug #673797 which was not fixed by my
previous patch.

I'm waiting for Ben Laurie to review this patch for me,
then I'll assign it to Guido to check it in.