o ROBUSTNESS/BUG FIX: createFrom(..., mode="copy") for AffymetrixCelFile
  would give an error on "No permission to modify existing file: ..."
  iff the source file had read-only permission.  This bug was introduced
  by changes to base::file.copy() in R (>= 2.13.0) [April 2011].
  Thanks to Taylor Raborn at Indiana University for reporting on this.