Fixed a bug that occurred under Windows only when using the ArffViewer from the command line or GUIChooser - Save as would fail to save the current set of instances and claim that the chosen file name already exists.

git-svn-id: https://svn.cms.waikato.ac.nz/svn/weka/trunk@9890 e0a1b77d-ad91-4216-81b1-defd5f83fa92
Merge remote-tracking branch 'upstream'