Correct pref name for retina iPad

The correct value in the prefs to start a retina iPad is "iPad Retina" (not "iPad (Retina)").  The test case is whether specifying "--retina" in addition to "--ipad" has any effect.

Tested with Xcode 5.0 on MacOSX 10.8 and Xcode 5.1 on MacOSX 10.9