Added an option to invert the selection - i.e randomly remove rather than select attributes.

git-svn-id: https://svn.cms.waikato.ac.nz/svn/weka@11153 e0a1b77d-ad91-4216-81b1-defd5f83fa92
Added an option to invert the selection - i.e randomly remove rather than select attributes.

git-svn-id: https://svn.cms.waikato.ac.nz/svn/weka@11154 e0a1b77d-ad91-4216-81b1-defd5f83fa92