Fix bug #7274075 Non-functional CheckedTextView on Nexus 7 Jelly Bean 4.1.1

This regression has been introduced by this Change: Ia846de16bbc54f0729608259aa4b530da9404245

- in CHOICE_MODE_SINGLE you need to clear the checked states before doing anything
- rename variables for better readability too

Change-Id: I89b4390e5ebb192ca280fea2c06f991b537a2870