title: Nant Fails on File::exists check
body: <p>I<code>m getting a problem in a Nant Build i</code>m running , 
  There is a part where i need to execute a file and then delete it , but only if the file exists , 
  But the script keeps failing</p>
  
  <p>****The relevant Script part :****</p>
  
  <pre><code>    &lt;do&gt;
          &lt;property name="lessfolder.parent" value="${directory::get-parent-directory(lessfile)}" /&gt;
          &lt;property name="lessfolder.parent.parent" value="${directory::get-parent-directory(lessfolder.parent)}" /&gt;
          &lt;property name="lessfolder.parent.parent.parent" value="${directory::get-parent-directory(lessfolder.parent.parent)}" /&gt;
          &lt;property name="cssfile" value="${path::get-file-name-without-extension(lessfile)}" /&gt;
          &lt;property name="sabatfiletest" value="${core.publish}\less\LessSaCompile.bat" /&gt;
          &lt;echo file="${sabatfiletest}" append="true"&gt;
            call ${less} "${lessfile}" &gt; "${lessfolder.parent.parent.parent}\SA_${cssfile}.css"
          &lt;/echo&gt;
        &lt;/do&gt;
      &lt;/foreach&gt;
      &lt;exec program="${core.publish}\less\LessCompile.bat"&gt;
      &lt;/exec&gt;
      &lt;sleep seconds="4" /&gt;
      &lt;exec program="${core.publish}\less\LessSubDomainCompile.bat"&gt;
      &lt;/exec&gt;
      &lt;sleep seconds="4" /&gt;
      &lt;exec program="${core.publish}\less\LessSaCompile.bat" if="${file::exists(sabatfiletest)}"&gt;
      &lt;/exec&gt;
      &lt;sleep seconds="4" /&gt;
      &lt;delete file="${core.publish}\less\LessCompile.bat" /&gt;
      &lt;delete file="${core.publish}\less\LessSubDomainCompile.bat" /&gt;
      &lt;delete file="${core.publish}\less\LessSaCompile.bat" if="${file::exists(sabatfiletest)}" /&gt;
    &lt;/target&gt;
  </code></pre>
  
  <p>****And The Error i`m getting  :****</p>
  
  <pre><code>Build Error: NAnt.Core.BuildException
  Property evaluation failed. Expression: ${file::exists(sabatfiletest)} ^^^^^^^^^^^^^
  in D:\Projects\Integration\Scripts\NAnt\iFOREX.Framework.BuildTFS.xml line: 725 col: 6
     at NAnt.Core.PropertyDictionary.EvaluateEmbeddedExpressions(String input, Location location, Hashtable state, Stack visiting)
     at NAnt.Core.PropertyDictionary.ExpandProperties(String input, Location location)
     at NAnt.Core.Element.AttributeConfigurator.InitializeAttribute(PropertyInfo propertyInfo)
     at NAnt.Core.Element.AttributeConfigurator.Initialize()
     at NAnt.Core.Element.InitializeXml(XmlNode elementNode, PropertyDictionary properties, FrameworkInfo framework)
     at NAnt.Core.Element.Initialize(XmlNode elementNode, PropertyDictionary properties, FrameworkInfo framework)
     at NAnt.Core.Element.Initialize(XmlNode elementNode)
     at NAnt.Core.Project.CreateTask(XmlNode taskNode, Target target)
     at NAnt.Core.Target.Execute()
     at NAnt.Core.Project.Execute(String targetName, Boolean forceDependencies)
     at NAnt.Core.Project.Execute()
     at NAnt.Core.Project.Run()
  </code></pre>