Extra root mortality transfer bug

[aldivi]

For forest and the rest of the land types (not savanna/woodland), mortality greater than the initial year is added (or subtracted if it is less than the initial, or at least it should be) to the soil c.
The difference that is added is incorrect (it is currently the difference between the initial year mortality carbon and the current year mortality carbon).
It should be the difference between the mortality calculated in the current year using the initial mortality fraction, and the mortality calculated in the current year using the current year mortality fraction.

[aldivi]

this reduced the amount of carbon added to soil due to varying mortality. it is apparent in shrubland and forest, and maybe desert (although i didn't check), so it shows up in the overall carbon and ghg absolute budgets. It isn't major, but it is a change. It had very little effect on the changes from baseline.