Don't cache contact list and T9 characters longer than the dialer's

lifetime.

- T9 characters may change if the user changes the OS language
- Contacts may change anytime by user's actions (add, modify, delete,
  sync)

Fixes http://code.google.com/p/cyanogenmod/issues/detail?id=6084

Change-Id: I171032b441e56dd2b7ce3c90535db4683fb79668