Merge branch 'be-openssl-drop-fd_is_set-v4'

This must fix some issues with bufferevent openssl layer + some cleanups.

* be-openssl-drop-fd_is_set-v4:
  be_openssl: don't use *_auto() in do_handshake() we can't have fd == -1 there
  be_openssl: don't call set_open_callbacks() if fd == -1
  be_openssl: introduce be_openssl_auto_fd() helper
  be_openssl: introduce set_open_callbacks_auto()
  be_openssl: get rid off hackish "fd_is_set", to fix some corner cases