Log Message:
Update lang/erlang to 18.1.

Some highlights of the release are:

- ssl: Add possibility to downgrade an SSL/TLS connection to a tcp
  connection, and give back the socket control to a user process.
- ssh: The following new key exchange algorithms are implemented:
  'ecdh-sha2-nistp256', 'ecdh-sha2-nistp384', 'ecdh-sha2-nistp521',
  'diffie-hellman-group14-sha1', 'diffie-hellman-group-exchange-sha1'
  and 'diffie-hellman-group-exchange-sha256'. This raises the
  security level considerably.
- kernel,stdlib,sasl: A mechanism for limiting the amount of text
  that the built-in error logger events will produce has been
  introduced. It is useful for limiting both the size of log files
  and the CPU time used to produce them.

Full release notes:

  http://www.erlang.org/download/otp_src_18.1.readme