adds support for base internationalization

If a pod uses base internationalization in it's resources files (.xibs, .storyboards) then this change will make sure external strings files are used when appropriate.   Recommended strategy that has worked for me is the following, my podspec contains the following resource line:

      s.resources    = "#{s.name}/**/*.{lproj,png,xib,storyboard}"

With **lproj** in the resources line, they will be included as folders in the Pods project.  While not ideal in that XCode does not recognize them as localization bundles, the change to the script will now instruct ibtool to use the external strings in Base.lproj and the language files rather than assuming the text is hardcoded.  

The important thing is that when doing this, do not include *.strings as a resource or it will copy the strings out of the lproj bundles into the root and further confuse XCode.