[TargetInstaller] Create unique hash instances for the build settings

Closes #1014

lib/cocoapods/installer/target_installer.rb

@@ -80,7 +80,7 @@ module Pod
           unless @target.build_configurations.map(&:name).include?(bc_name)
             build_config = project.new(Xcodeproj::Project::XCBuildConfiguration)
             build_config.name = bc_name
-            settings = @target.build_settings(type.to_s.capitalize)
+            settings = @target.build_settings(type.to_s.capitalize).dup
             build_config.build_settings = settings
             target.build_configurations << build_config
           end

spec/unit/installer/target_installer_spec.rb

@@ -116,6 +116,12 @@ module Pod
         @project.targets.first.build_configurations.map(&:name).sort.should == %w{ AppStore Debug Release Test }
       end
 
+      it "it creates different hash instances for the build settings of various build configurations" do
+        @installer.install!
+        build_settings = @project.targets.first.build_configurations.map(&:build_settings)
+        build_settings.map(&:object_id).uniq.count.should == 4
+      end
+
       it "does not enable the GCC_WARN_INHIBIT_ALL_WARNINGS flag by default" do
         @installer.install!
         @installer.library.target.build_configurations.each do |config|