Enable Date in stepsArray and bindIndexForStepsArray: false

[ValentinH]

Steps to reproduce

1. create a stepsArray with Date objects
2. without using the bindIndexForStepsArray option defaults to false)

Demo: http://jsfiddle.net/teLLg7e2/

Actual behaviour

It doesn't work because comparing dates with == or === is incorrect: http://stackoverflow.com/questions/492994/compare-two-dates-with-javascript . Thus, we should add a special test with angular.isDate() to handle this case.