add --stdout/stderr option to lines.rb

to make it easier to generate test output
on both stdout and stderr

t/bin/lines.rb

@@ -1,6 +1,14 @@
 #!/usr/bin/ruby
 
-for line in ARGV
+out = STDOUT
-    puts line
-end
 
+for line in ARGV
+    case line
+    when "--stdout"
+        out = STDOUT
+    when "--stderr"
+        out = STDERR
+    else
+        out.puts(line)
+    end
+end