adding a "original-directory" parameter

[sorawee]

Some environments set current-directory such as raco test. While I understand the rationale and thinks this is a good default behavior, sometimes I really need the information of the actual current directory, and currently it seems there's no way to do that. For instance:

raco test ++args ./foo/bar.txt sub/main.rkt

specifies ./foo/bar.txt relative to ., not sub, making the script not functional as expected.

@samth suggests that there should be a parameter that really sets to the actual current directory.