Add support for the SupportedUserInterfaceIdioms attribute.
Merge pull request #263 from nschum/feature/SupportedUserInterfaceIdioms

Add support for the SupportedUserInterfaceIdioms attribute.
Fix multiple selection with numeric values.

Apple's Settings.app turns numeric value strings into numbers.
That means updateCheckedItem never found a match.

This happens with "MUL_VAL" in the sample app, for example.