UPGRADE: http pak.

    REFACTOR: Change HttpStage open to take a return status code.

    If HttpStage.open gets an error, its close() callback should not be invoked. To handle this, open must return a stat
    If the handler open() calls httpError, the passHandler needs to be used instead thereafter.
    Also need more robust pendingFinalize if httpError is called before the pipeline is fully constructed.
TEST: Shrink memory footprint of unit tests.

Refactor some "big" tests to explicitly yield.
UPGRADE: mpr pak

Fix cache trace.