Log Message:
Update security/stunnel to 5.56. Upstream says

### Version 5.56, 2019.11.22, urgency: HIGH
* New features
  - Various text files converted to Markdown format.
* Bugfixes
  - Support for realpath(3) implementations incompatible
    with POSIX.1-2008, such as 4.4BSD or Solaris.
  - Support for engines without PRNG seeding methods (thx to
    Petr Mikhalitsyn).
  - Retry unsuccessful port binding on configuration
    file reload.
  - Thread safety fixes in SSL_SESSION object handling.
  - Terminate clients on exit in the FORK threading model.