call `setTheme` before `super.onCreate`

It's optional for ics+, however, I'm glad if you can merge it, which
will fix possibble conflict in following back-porting.

The custom theme won't apply after the call of `super.onCreate`.
It seems a bug in Android 2.3, and ICS+ fixes it.
For more information, please visit:
https://code.google.com/p/android/issues/detail?id=4394