Record the states of failing OR connections

This code lets us record the state of any outgoing OR connection
that fails before it becomes open, so we can notice if they're all
dying in the same SSL state or the same OR handshake state.

More work is still needed:
  - We need documentation
  - We need to actually call the code that reports the failure when
    we realize that we're having a hard time connecting out or
    making circuits.
  - We need to periodically clear out all this data -- perhaps,
    whenever we build a circuit successfully?
  - We'll eventually want to expose it to controllers, perhaps.

Partial implementation of feature 3116.

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