Fixup: use proper variable in printk()->TRACE() integration
Add config option for optional BUG() on migration failure

By default, the migration failure code should be noisy, otherwise it's
too easy to miss problems. However, on real hardware, it can be
convenient to be permissive. So make the behavior configurable.

While touching this code, let's also raise the threshold for
complaining about a problem to one second, since QEMU sometimes
produces weird latency spikes that could trigger this prematurely.
binomial heap: BUG_ON() node deletion from wrong heap

When trying to delete a node from a heap that it doesn't contain it,
the result is typically a NULL pointer bug. Let's make the resulting
crash a littlebit more expressive to give users a hint as to what
might be the problem.