This adds a simple API to have your back stack automatically
shown as bread crumbs in the action bar. Introduces some APIs
to retrieve the current back stack.
Also fix a little bug in the "activated" state where it was
being propagated down the hierarchy as "selected". :p And from
that, fix the standard colors to be reasonable when in the
activated state.
Finally PreferenceActivity is updated to take advantage of
bread crumbs to show your place in the preferences.
Change-Id: I9d633bedf8d7c6e4ed9b25cb9698faa66c7dd9a4
c6669ca632