Avoid creating duplicate references for resources.

lib/cocoapods/installer/target_installer/pod_target_installer.rb

@@ -79,7 +79,7 @@ module Pod
           next unless target.requires_frameworks?
 
           resource_refs = file_accessor.resources.flatten.map do |res|
-            project.new_file(res.relative_path_from(project.path.dirname))
+            project.reference_for_path(res)
           end
 
           resource_refs += project.products_group.files.select do |product_ref|

spec/unit/installer/target_installer/pod_target_installer_spec.rb

@@ -21,6 +21,9 @@ module Pod
         file_accessor.source_files.each do |file|
           @project.add_file_reference(file, group)
         end
+        file_accessor.resources.each do |resource|
+          @project.add_file_reference(resource, group)
+        end
 
         @pod_target = PodTarget.new([@spec], @target_definition, config.sandbox)
         @pod_target.stubs(:platform).returns(Platform.new(:ios, '6.0'))