TabWidget orientation

TabWidget orientation specified in tab_content.xml instead of TabWidget.java.
Generally, the orientation of the TabWidget should be set in xml-files
and not in TabWidget.java. A sub class of TabActivity may call setContentView()
using a custom layout where the TabWidget orientation is vertical.
This is the case in the UI Enablers Bottom Tab feature, for landscape
display orientation.

Change-Id: Ia677441a0af96a8d2ab47ef3298eb440c34924f6