Clarify failonerror.

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@277148 13f79535-47bb-0310-9956-ffa450edef68

docs/manual/CoreTasks/copy.html

@@ -93,7 +93,7 @@ operation as <a href="../CoreTypes/filterset.html">filtersets</a>
   </tr>
   <tr>
     <td valign="top">failonerror</td>
-     <td valign="top">Log a warning message, but do not stop the
+     <td valign="top">If false, log a warning message, but do not stop the
        build, when the file to copy does not exist or one of the nested
        filesets points to a directory that doesn't exist or an error occurs
        while copying.