add documentation for <cvs>'s failonerror attribute.

PR: 4205


git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@269810 13f79535-47bb-0310-9956-ffa450edef68

docs/manual/CoreTasks/cvs.html

@@ -80,6 +80,12 @@ preferred over the <i>checkout</i> command, because of speed.</p>
     <td valign="top">Password file to read passwords from.</td>
     <td align="center" valign="top">No, default file ~/.cvspass.</td>
   </tr>
+  <tr>
+    <td valign="top">failonerror</td>
+    <td valign="top">Stop the buildprocess if the command exits with a
+      returncode other than 0. Defaults to false</td>
+    <td align="center" valign="top">No</td>
+  </tr>
 </table>
 <h3>Examples</h3>
 <pre>  &lt;cvs cvsRoot=&quot;:pserver:anoncvs@jakarta.apache.org:/home/cvspublic&quot;