Generates too many nodes, sometimes.

[luke-clifton]

@conal as we discussed at LambdaJam, I've collected an example where the circuit generates more nodes than it needs to, along with the modifications required to convince the output to be in the form I desired (fewer nodes).

https://github.com/luke-clifton/concat/blob/shrinkable/test/Examples.hs#L184 generates the following

when I would really rather it generated this.

Which was actually generated by the following.
https://github.com/luke-clifton/concat/blob/shrinkable/test/Examples.hs#L192

ping @lancelet @thsutton @robbiemcmichael