back-ported to gingerbread, denpends on FragmentActivity and PreferenceFragment

The binary will grow from 30K to ~300K (most size is android-support-library)

FragmentActivity (627K~): android support library
http://developer.android.com/tools/support-library/index.html

PreferenceFragment (~9K): A reflect call for the latest android.preference.PreferenceFragment
Source: https://github.com/liudongmiao/preference-fragment-compat