support project_dir_path in file_ref.real_path

[WeijunDeng]

Xcodeproj/lib/xcodeproj/project/object/helpers/groupable_helper.rb

Line 156 in 29cd082

object.project.project_dir

if ref.source_tree == "SOURCE_ROOT"
    # fix bugs in https://github.com/CocoaPods/Xcodeproj/blob/29cd0821d47f864abbd1ca80f23ff2aded0adfed/lib/xcodeproj/project/object/helpers/groupable_helper.rb#L156
    # support CMake generated projects with project_dir_path
    file_path = (ref.project.project_dir + ref.project.root_object.project_dir_path + ref.path).to_s
else
    file_path = ref.real_path.to_s
end