Fix VPO_UNMANAGED handling in vm_page_reclaim_run().

[markj]

Summary

When we allocate a replacement page we must clear VPO_UNMANAGED, since
we only ever reclaim pages from managed objects. vm_page_replace() does
not handle this for us.

Sprinkle some assertions to help catch this sort of issue.

Test Plan

Peter is testing this.

[kib]

sys/vm/vm_page.c

3676

I think this assert is not useful, it is tautologically repeats the condition that resulted in this branch.

3680

same

[markj]

sys/vm/vm_page.c

3676

Ugh, for some reason I read the condition as (m->object->flags & OBJ_UNMANAGED) == 0.

[markj]

Add a non-tautological assertion to vm_page_free_prep().