Fixed typo None/True in Setting definition

Ignore-this: d0139433e121181a8d5dccf8904d3bdb

darcs-hash:20090316220420-1e3d8-2f44d0c393dbd2f3f59d2ab29fce2fe54ece2236
Made Setting descriptor more robust

Ignore-this: aee57f9b0ff7b6eb435f2ae12aa79979

darcs-hash:20090316220442-1e3d8-c8438b7fa409541cb5c08a42bb603462f15a21bd