Avoid reprinting nodes whose children can be reprinted.
Avoid reprinting nodes whose children can be reprinted.

This reduces the running time of the identity tests from 6.9s to 2.5s, which goes a long way towards addressing issue #18.

stefanpenner/recast,kyldvs/recast,rwaldron/recast,cpojer/recast,benjamn/recast,marcioj/recast,ipeychev/recast,benjamn/recast,fkling/recast,benjamn/recast,kassens/recast,ersengultepe/recast,shumov/recast