Kernel::signal_context_kill can be used by any program to halt the processing
of a signal context synchronously to prevent broken refs when core destructs
the according kernel object. In turn, Kernel::bin_signal_context doesn't block
anymore and destructs a signal context no matter if there are unacknowledged
signals. This way, cores entrypoint doesn't depend on signal acks of a
untrustworthy client anymore.
ref #989
1c8c30e1f4