#34 Add ability to use ant core types in the GroboUtils ant task

[Michael]

It would be nice to be able to use ant core types such
as fileset, dirset and patternset within the GroboUtils
ant tasks.

For example, in the grobo-report task it would be nice to
use the ant dirset core type rather than multiple srcdir
elements. This gives a little more flexibility in specifying
source directories using wildcards.