Rewrite flex's computed value to be more abstract to properly capture what's intended.

Author: tabatkins

css3-flexbox/Overview.html

@@ -1194,9 +1194,9 @@ <h2 id=flexibility><span class=secno>7. </span> Flexibility: the &lsquo;<a
     <tr>
      <th>Computed Value:
 
-     <td>for &lsquo;<code class=css>none</code>&rsquo;, &lsquo;<code
-      class=css>0 0 auto</code>&rsquo;. For all other values, the specified
-      value, with relative lengths converted to absolute lengths.
+     <td>Two integers for positive and negative flex, and either an absolute
+      length (if &lt;preferred-size> is given as a &lt;length>) or the
+      specified value for &lt;preferred-size>.
 
     <tr>
      <th>Media:
@@ -2640,9 +2640,9 @@ <h2 class=no-num id=property>Property index</h2>
 
      <td>no
 
-     <td>for &lsquo;none&rsquo;, &lsquo;0 0 auto&rsquo;. For all other
-      values, the specified value, with relative lengths converted to
-      absolute lengths.
+     <td>Two integers for positive and negative flex, and either an absolute
+      length (if &lt;preferred-size> is given as a &lt;length>) or the
+      specified value for &lt;preferred-size>.
 
      <td>visual
 

css3-flexbox/Overview.src.html

@@ -587,7 +587,7 @@ <h2 id='flexibility'>
 			<td>no
 		<tr>
 			<th>Computed Value:
-			<td>for ''none'', ''0 0 auto''.  For all other values, the specified value, with relative lengths converted to absolute lengths.
+			<td>Two integers for positive and negative flex, and either an absolute length (if &lt;preferred-size> is given as a &lt;length>) or the specified value for &lt;preferred-size>.
 		<tr>
 			<th>Media:
 			<td>visual