Add some special constants for "unintialized" values.
Add some special constants for "unintialized" values.

These are uninitialized in the sense that our program
has not set the value yet (so shouldn't use the value).

tobeycarman/dvm-dos-tem,tobeycarman/dvm-dos-tem,tobeycarman/dvm-dos-tem,tobeycarman/dvm-dos-tem,tobeycarman/dvm-dos-tem,tobeycarman/dvm-dos-tem