m_ssl_openssl Clear the error queue before every SSL_* call
m_ssl_openssl Enable single (EC)DH use and disable SSL v2

Options enabled:
- SSL_OP_NO_SSLv2
- SSL_OP_SINGLE_DH_USE
- SSL_OP_SINGLE_ECDH_USE (if it exists)

Partial backport of #856 by @jvehent
m_ssl_openssl Disable session caching and session tickets