More fragment stuff:

- New startActivityForResult() API.
- Fragments now should have the correct lifecycle while hanging around
  in the back stack (not being destroyed and re-created).
- Rework of state save/restore to make it simpler and better.  In theory
  now any fragment (including layout and others in the hierarchy) can
  now be retained across config changes, though this hasn't been tested.

Change-Id: I2a7fe560e14e567f5675a2f172a23fca67b3e97f