Fixed the fixup rules to ignore runs of solely whitespace.

Author: tabatkins

css3-flexbox/Overview.html

@@ -511,7 +511,9 @@ <h2 id=flex-items><span class=secno>4. </span> Flexbox Items</h2>
    <li>Atomic inline-level children of flexbox
 
    <li>Contiguous run of non-replaced inline children, wrapped into an
-    anonymous block box
+    anonymous block box. If this would produce an anonymous box filled only
+    with white-space, the box is not generated, and the whitespace is removed
+    from the box tree.
   </ol>
 
   <p>Some values of &lsquo;<code class=property>display</code>&rsquo; trigger

css3-flexbox/Overview.src.html

@@ -180,7 +180,7 @@ <h2 id='flex-items'>
 
 		<li>Atomic inline-level children of flexbox</li>
 
-		<li>Contiguous run of non-replaced inline children, wrapped into an anonymous block box</li>
+		<li>Contiguous run of non-replaced inline children, wrapped into an anonymous block box.  If this would produce an anonymous box filled only with white-space, the box is not generated, and the whitespace is removed from the box tree.</li>
 	</ol>
 
 	<p>Some values of 'display' trigger "fixup" to ensure a sensible tree structure.  For example, a lone ''table-cell'' box is fixed up by generating ''table'' and ''table-row'' boxes around it.  This fixup must occur <em>before</em> a flexbox's contents are checked to see if it's necessary to generate anonymous flexbox items.</p>