Make hipe non-upgradable

The reason for this is that if you are running a system with native
compiled code, then you will have major problems with soft upgrade
and the only reasonable way to go is to restart your emulator.

Currently there is no instruction that will force ONLY a restart of
the emulator, so the solution would be to hand write a relup with
only a restart_emulator instruction. By letting hipe.appup be empty,
systools will complain and not generate a relup - which should
indicate that you might have to write your relup by hand.
Add documentation for test_server:appup_test/1