remove Stream#headDefined. use nonEmpty
remove Stream#headDefined. use nonEmpty

scala/scala,scala/scala,scala/scala,scala/scala,martijnhoekstra/scala,martijnhoekstra/scala,martijnhoekstra/scala,scala/scala,lrytz/scala,scala/scala,lrytz/scala,lrytz/scala,lrytz/scala,martijnhoekstra/scala,martijnhoekstra/scala,lrytz/scala,martijnhoekstra/scala,lrytz/scala