clean dir in ccnet prebuild task
<!--
Pre build tasks
User powershell to CLEAN the directory, it doesn't remove the parent as this will be in use by cc.net
-->
<prebuild>
<exec>
<executable>powershell.exe</executable>
<buildArgs><![CDATA[-command "& {if( [System.IO.Directory]::Exists($pwd) ){dir $pwd | ri -recurse -force}}"]]></buildArgs>
</exec>
</prebuild>