2016-10-10: do not print space before function which returns #f. three-witches-space-in-name

do not print space before function which returns #f.

diff --git a/examples/enter-three-witches.w b/examples/enter-three-witches.w
--- a/examples/enter-three-witches.w
+++ b/examples/enter-three-witches.w
@@ -65,8 +65,9 @@ define-syntax say-words
         syntax-case x ()
             : _ (((word words ...))) (() lines ...)
               #` begin
-                 show " "
-                 show : ->string `word
+                 when : not : equal? `word #f
+                   show " "
+                   show : ->string `word
                  say-words (((words ...))) (() lines ...)
             : _ ((())) (() lines ...)
               #` begin