GDS_FILE property in the same way that it handles changes to the
FIXED_BBOX property, by setting or clearing the associated flag
bit in the cell. Otherwise, it becomes impossible to make a
cell writeable, as it always has some belief that it is still
attached to a specific GDS file. Corrected an error in the
"gds" ("calma") command parsing that switched the callbacks for
the "noduplicates" and "nodatestamp" options.