function lookupValue(property, objects) {
    for (var i = 0; i < objects.length; ++i) {
      if (property in objects[i]) {
        return objects[i][property];
      }
    }
  }
Given the name of a property, iterates over a list of objects until finding
one with the given property. Returns the first value found.

This is to allow the options supplied to a call to
#comprehensiveSequenceTest to include properties at the top level, and also
to override those at the case level.