Enhance the gunzip task and the BUnzip2 task to support filesets, patternsets, 
and the overwrite attribute.

Ideally the additional features would be consistent with the Unzip task. With 
the same attributes and elements with the same rules applied across UnZip, 
GunZip and BUnZip2. 

Possibly all three tasks could be merged into one task with an attribute for 
which type of unzip to apply, to otherwise default according to the file 
extension.


An example would be:

<gunzip dest="${tools.home}" overwrite="true">
    <patternset>
        <include name="**/*.java"/>
        <exclude name="**/Test*.java"/>
    </patternset>
    <fileset dir=".">
        <include name="**/*.gz"/>
        <exclude name="**/tmp*.gz"/>
    </fileset>
</unzip>