AttributeLocator now uses BitSet and ArrayList rather than Vector. In particular, BitSet is used instead of Vector<Byte>, resulting in *HUGE* space savings when using filters to process/produce large-dimensional datasets! Also removed occurrences of DenseInstance in error messages originating in AbstractInstance. Finally, improved efficiency of insertAttributeAt() and deleteAttributeAt() in Instances and added new method replaceAttributeAtt(), replacing almost all calls of insertAttributeAt()/deleteAttributeAt() in WEKA with calls of replaceAttributeAt().

git-svn-id: https://svn.cms.waikato.ac.nz/svn/weka@10649 e0a1b77d-ad91-4216-81b1-defd5f83fa92