* Make vm::unmap atomic, squash the memory unmapping process inside this function while still using the same VM mutex ownership.
* Make vm::unmap not fail due to random vm::get calls, shared_ptr reference count is no longer a condition.
* Fix sys_mmapper_free_address spuriously failing with EBUSY due to random vm::get calls.
* Fix sys_vm_unmap race condition due to non-atomic vm::unmap.
* Add an optional verification block ptr arg to vm::unmap, used by patches.