describe difference of <dirname> and unix dirname

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@451692 13f79535-47bb-0310-9956-ffa450edef68

docs/manual/CoreTasks/dirname.html

@@ -36,6 +36,11 @@ the last path element. If the specified file is a path that ends in a
 filename, the filename will be dropped. If the specified file is just
 a filename, the directory will be the current directory.
 </p>
+  <p>
+    <em>Note:</em> This is not the same as the UNIX dirname command, which is
+    defined as "strip non-directory suffix from filename". &lt;dirname&gt;
+    determines the full directory path of the specified file.
+  </p>
 <h3>Parameters</h3>
 <table border="1" cellpadding="2" cellspacing="0">
   <tr>