boutiques dir maker with file list

[MontrealSergiy]

sometimes one might wish put files in the same folder using

        "BoutiquesInputSubdirMaker": {
            "previous_results": {
                "dirname": "ReconstructedDir"
            }
        }

Yet if previous_results input is list, invocation file the task setup fails, as in the invocation build by CBRAIN "previous_results" is a string rather than array. It is extension, but also marked as a bug as IMHO the module should at least log some warning explaining that file lists are not supported.

[MontrealSergiy]

I thought it might helpful with some group analysis tool, which seems low priority now. If it is too costly to add file list support (e.g. along the lines of 1b5ba0b ), we could issue an error message or a the least a warning when user supplies file list