fix batch:
 1. fix heca_write_fault to remove hpc from tree in edge cases that
    dealloc it before retrying
 2. document an edge case in immediate gup that we do not solve (but
    also probably should not solve)
 3. change pte_unmap_unlock to spin_unlock when pte_unmap not needed
Merge pull request #42 from roeitell/dev

Stabilize the new push path