OpenVPN 2.3.18 release

2017.09.25 -- Version 2.3.18
Antonio Quartulli (1):
      crypto: correct typ0 in error message

Steffan Karger (2):
      Deprecate --ns-cert-type
      Fix bounds check in read_key()

Szilárd Pfeiffer (1):
      OpenSSL: Always set SSL_OP_CIPHER_SERVER_PREFERENCE flag