class Xcodeproj::Project::Object::AbstractBuildPhase

def add_file_reference(file_ref, avoid_duplicates = false)
  if avoid_duplicates && existing = build_file(file_ref)
    existing
  else
    build_file = project.new(PBXBuildFile)
    build_file.file_ref = file_ref
    files << build_file
    build_file
  end
end