Fix 2088: Do not cut off drop-down deck names in landscape mode

I really don't understand how GitHub gets away with their simple [drop-down layout](https://github.com/github/android/blob/master/app/res/layout/org_dropdown_item.xml) for their Android app. Anyway, here's some magic to fix [2088](https://code.google.com/p/ankidroid/issues/detail?id=2088), basically taken from `support_simple_spinner_dropdown_item` found in the appcompat package.