Fix Patched.knownSize, and exploit it in Patched.isEmpty
Fix Patched.knownSize, and exploit it in Patched.isEmpty

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