Path expression on very large object causes RangeError

[andrew-coleman]

When mapping over objects that contain a large number of properties (>> 100000), the evaluator throws the js error RangeError: Maximum call stack size exceeded.

This is a bug in the flattening logic caused by the use of Array.prototype.push.apply to join arrays and is related to the known issue nodejs/node#27732.

This bit of code needs rewriting.