Create cost allocation map output

Author: anitagraser

python/plugins/processing/algs/grass7/description/r.cost.raster.txt

@@ -8,4 +8,5 @@ ParameterBoolean|-n|Keep null values in output raster layer|True
 ParameterNumber|max_cost|Maximum cumulative cost|0|None|0
 ParameterNumber|null_cost|Cost assigned to null cells. By default, null cells are excluded|None|None|0
 ParameterNumber|memory|Maximum memory to be used in MB|0|None|300
-OutputRaster|output|Cumulative cost
+OutputRaster|output|Cumulative cost
+OutputRaster|nearest|Cost allocation map