Fix grammar in unknown sources dialog. issue 1938

    <!-- Applications settings screen, setting check box title. If checked, the system allows installation of applications that are downloaded from random places, such as web sites.  -->

    <string name="install_applications">Unknown sources</string>

    <!-- Applications settings screen, setting check box summary.  This is the summary for "Unknown sources" checkbox  -->

    <string name="install_unknown_applications">Allow install of non-Market applications</string>

    <string name="install_unknown_applications">Allow installation of non-Market applications</string>

    <!-- Applications settings screen, message text of alert that appears if user selects the "Unknown sources" check box -->

    <string name="install_all_warning">Your phone and personal data are more vulnerable to attack by applications

 from unknown sources. You agree that you are solely responsible for any