Changeset 11088:e4b173785c24
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ruby: simple network: store Switch* in PerfectSwitch and Throttle
There are two reasons for doing so:

a. provide a source of clock to PerfectSwitch. A follow on patch removes sender
and receiver pointers from MessageBuffer means that the object owning the
buffer should have some way of providing timing info.

b. schedule events.  A follow on patch removes the consumer class.  So the
PerfectSwitch needs some EventManager object to schedule events on its own.