add utility method to determine if we are running on a simulator.

I found I had to vary my test script slightly between target and simulator (found a bug in apple's simulator) but did not see any utility method to detect if I was running on simulator or not.  So I added this feature.  I tried to get pod to point to my own repo without success -- I am new to the pod system.  Whilst manually making the code change here, and also on top of pod 1.01 version of tuneup_js, only the manual edit on top of 1.01 has been tested.

I've never done a git pull request thing before on github -- I hope this information is sufficient for your evaluation.