summary: Correct height of pipes denoting length

* src/current/include/calc-display.xsl
  (c:sum[@of], c:length-of): Add `\left', `\right'.
* src/current/summary.xsl: Update "N.B." section.

src/current/include/calc-display.xsl

@@ -167,9 +167,9 @@
   <xsl:if test="./c:*">
     <!-- the upper limit of the summation will be denoted by #S, where S is the
          symbol for a given set -->
-    <xsl:text>^{|</xsl:text>
+    <xsl:text>^{\left|</xsl:text>
       <xsl:copy-of select="$symbol" />
-    <xsl:text>|-1}</xsl:text>
+    <xsl:text>\right|-1}</xsl:text>
   </xsl:if>
 
   <!-- if no children are provided, just sum @of -->
@@ -711,9 +711,9 @@
 
 
 <xsl:template match="c:length-of">
-  <xsl:text>|\left(</xsl:text>
+  <xsl:text>\left|\left(</xsl:text>
     <xsl:apply-templates select="./c:*[1]" />
-  <xsl:text>\right)|</xsl:text>
+  <xsl:text>\right)\right|</xsl:text>
 </xsl:template>
 
 <xsl:template match="c:cons">

src/current/summary.xsl

@@ -2112,7 +2112,7 @@
 
       <dt>Counting Vectors</dt>
       <dd>
-        Let \(|V|\) = the number of values within the vector \(V\); this notation is
+        Let \(\left|V\right|\) = the number of values within the vector \(V\); this notation is
         used within certain summations. You may also see the following notations:
 
         <ul>
@@ -2122,7 +2122,7 @@
             count the number of swimming pools).
           </li>
           <li>
-            \(\sum_{k=0}^{|V|-1} 1\) to count the number of values in vector \(V\).
+            \(\sum_{k=0}^{\left|V\right|-1} 1\) to count the number of values in vector \(V\).
           </li>
         </ul>
       </dd>