BUG/MEDIUM: ssl: Prevent ssl error from affecting other connections.

BUG/MEDIUM: ssl: Prevent ssl error from affecting other connections.

J. Maurice reported that ssllabs.com test affects unrelated
legitimate traffic and cause SSL errors and broken connections.

Sometimes openssl store read/write/handshake errors in a global stack. This
stack is not specific to the current session. Openssl API does not clean the
stack at the beginning of a new read/write. And the function used to retrieve
error ID after read/write, returns the generic error SSL_ERROR_SSL if the
global stack is not empty.

The fix consists in cleaning the errors stack after read/write/handshake
errors.