* raimo/diffserv-socket-option/OTP-13582:
  Tune 'tclass' semantics
  Implement IPV6_TCLASS

* bjorn/erts/on_load/ERL-240/OTP-13893:
  erts: Add nif_SUITE:t_on_load
  erts: Improve nif_SUITE:upgrade test
  Don't leak old code when loading a modules with an on_load function

Normally, calling code:delete/1 before re-loading the code for a
module is unnecessary but causes no problem.

But there will be be problems if the new code has an on_load function.
Code with an on_load function will always be loaded as old code
to allowed it to be easily purged if the on_load function would fail.
If the on_load function succeeds, the old and current code will be
swapped.

So in the scenario where code:delete/1 has been called explicitly,
there is old code but no current code. Loading code with an
on_load function will cause the reference to the old code to be
overwritten. That will at best cause a memory leak, and at worst
an emulator crash (especially if NIFs are involved).

To avoid that situation, we will put the code with the on_load
function in a special, third slot in Module.

ERL-240

* lukas/kernel/os_cmd_fix_stdin_close/OTP-13867:
  kernel: Close stdin of commands run in os:cmd

This is needed when running programs that only exit when
stdin has been closed, e.g. 'more'.

* maint-19:
  Updated OTP version
  Prepare release
  erts: Make sure to flush potential exit message