Don't install packages where we have multiple, conflicting
<uses-permission> lines for the same permission.
For example, a package which contains:
<uses-permission android:name="android.permission.INTERNET" android:required="false" />
<uses-permission android:name="android.permission.INTERNET" android:required="true" />
will now fail to install.
In addition, this change slightly refactors the code, and creates a new
parseUsesPermission() method.
Change-Id: I0f4bb8b51dc4a0c5b73458a70f706e19829275d2
73f2d3c79e