fix checksum checking error in download script
fix checksum checking error in download script

- the checksum regex had a bug with the initial file check
- if a file had already been downloaded the script was supposed to check
  the md5sum before trying to download it again. The bug prevented the
  script from seeing that the file was correct and dowload it again.
- the split statement is a little cleaner. Also advoids the need to
  `chomp` the string before the regex

dpastling/plethora,dpastling/cnv_pipeline,dpastling/plethora,dpastling/cnv_pipeline,dpastling/plethora