#567 remove use of ant-contrib <var unset="true" ../>

[Alex Honor]

As of Ant 1.8, the var task is problematic. The unset='true' option which should unset the property does not seem to work. Here's a typical pattern in existing handlers:
<var name="someprop" unset="true"/>
<property name="someprop" value="new value"/>

One could use the CTL property-expand task like so:
<property-expand property="someprop" input="new value" override="true"/>

There are also new alternatives like Ant's new "local" task.

[Moses Lei]

I think we should figure out why this no longer works, instead. Perhaps we just need to update ant-contrib?

The var task is pretty useful and it's used quite often.

[Alex Honor]

The "newest" antcontrib jar (1.0b5) was tested but suffers the same problems due to the heavily refactored property mgt in Ant 1.8