fixes combinations to work despite clang bug
fixes combinations to work despite clang bug

jkhoogland/cppitertools,tempbottle/cppitertools,jkhoogland/cppitertools,jkhoogland/cppitertools,tempbottle/cppitertools,ryanhaining/cppitertools,ryanhaining/cppitertools,ryanhaining/cppitertools,tempbottle/cppitertools