Dataverse creates plain-text, preservation-friendly copies of certain
file formats (some of which are proprietary, such as Stata or SPSS) and
this .tab (tab-separated) file is downloaded unless you supply
`format=original`, which is what this pull request does.
The original filename (e.g. foo.dta, a Stata file) comes from
`originalFileName`, which is only populated when the preservation copy
(e.g. foo.tab) has been successfully created.
Additional variables were created to distinguish between `filename`,
`original_filename`, and `filename_with_path`. If `original_filename`
is available, it's the right one to use.
To allow the tests to continue passing, the query parameters are now
removed so just the file id can be cast as an int.
Philip Durbin