Removed unnecessary set series hack

The io->SetSeries + reader->Modified() code works to properly set the
series of the underlying reader. Removed the code that would insert
@-annotated series indices into the input file name.
Added WriteSCIFIO flag to itkSCIFIOImageIOTest

The -w or --write-scifio flag can now be used to force the use of the
SCIFIOImageIO when writing, instead of the default ImageIO package.