ListView uses the _id column for some operations, including
onSave/RestoreInstanceState, and if the column contains negative values
they don't work as expected. The same assumption seems to be in other places
as well, so let's just avoid using negative IDs.
With this CL we now use two different IDs, one for ListView, which will
never be negative, and the other for us, the actual mailbox ID.
Bug 3049315
Change-Id: I263b4895212b5f8bb80c98acaf5c4eccd0bfef55
9b5001a34c