Cobertura task should be able to specify included/excluded classes

There should be an option to specify included/excluded classes in Cobertura tasks, just like in Cobertura Ant task:
http://cobertura.sourceforge.net/anttaskreference.html

There are often situations where we don't want some classes to appear on Cobertura reports (generated code, helper classes used only for unit tests etc.)

Currently there are only hardcoded includes in lib/buildr/cobertura.rb, like
ant.include :name=>"*/.class"
ant.include :name=>"*/.java"