Document the do-nothing-if-exist behaviour of <mkdir>

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@462786 13f79535-47bb-0310-9956-ffa450edef68

docs/manual/CoreTasks/mkdir.html

@@ -27,7 +27,7 @@
 <h2><a name="mkdir">Mkdir</a></h2>
 <h3>Description</h3>
 <p>Creates a directory. Also non-existent parent directories are created, when
-necessary.</p>
+necessary. Does nothing if the directory already exist.</p>
 <h3>Parameters</h3>
 <table border="1" cellpadding="2" cellspacing="0">
   <tr>
@@ -50,4 +50,3 @@ necessary.</p>
 
 </body>
 </html>
-