export function error reporting
A user tried to export a data package to a directory that she did not have permission to write in (a drive mapped with smb).
Morpho's response was a message window: "Some problem with saving data files has occurred" (click OK), followed by a second message window: "Package export complete"
1. Morpho should report a usable message for the problem, and
2. should not follow up with the same message it uses for successful exports.