Some small comment cleanups
Remove -2 as an error code

The error code is never checked.

The methods for handling the error are not implemented.

The error is unlikely to occur.

The error can be prevented by using the correct data types.
Remove references to unused error code

Was always just demoted to -1 anyway

If we really care about request numbers > int32 we'll just use int64
Merge pull request #402 from OttoAllmendinger/pr-remove-minus2

Remove -2 error code