This reverts commit 636d1104, reversing
changes made to b6309bbd.

# Conflicts:
#	lib/cocoapods/generator/xcconfig/xcconfig_helper.rb
#	lib/cocoapods/installer/xcode/pods_project_generator/file_references_installer.rb
#	spec/unit/installer/xcode/pods_project_generator/file_references_installer_spec.rb
#	spec/unit/target/build_settings/pod_target_settings_spec.rb