getlantern/lantern#1937 Limited rate of redialing

No.  There are two points at which we can receive a stop:

- We're looping and failing to dial successfully.  This is handled by the first select
- We've dialed successfully, and we're blocked waiting to submit our connection to p.connCh (pending the client actually consuming from p.connCh).  Once the conn is submitted to p.connCh, it's in the client's hands and it's the client's responsibility to close it.  If we receive a stop at this point, the pool needs to close the connection because no client even received it.

The unit test actually exercises both of these stops, and you can see that both are covered in the [coverage report](https://coveralls.io/files/339205934)