If and Unless on all tasks/nested elements

# If And Unless

Since Ant 1.9.1, it is possible to add if and unless attributes on all tasks and nested elements using special namespaces.

In order to use this feature you need to add the following namespace declarations

    xmlns:if="ant:if"
    xmlns:unless="ant:unless"

The `if` and `unless` namespaces support the following 3 conditions:

true
  true if the value of the attribute evaluates to true
blank
  true if the value of the attribute is null or empty
set
  true if the specified property is set

    <project name="tryit"
     xmlns:if="ant:if"
     xmlns:unless="ant:unless">
     <exec executable="java">
       <arg line="-X" if:true="${showextendedparams}"/>
       <arg line="-version" unless:true="${showextendedparams}"/>
     </exec>
     <condition property="onmac">
       <os family="mac"/>
     </condition>
     <echo if:set="onmac">running on MacOS</echo>
     <echo unless:set="onmac">not running on MacOS</echo>
    </project>