Watershed tool should default to the extent of the flow direction layer not the pour points layer

Idea created by tomdilts on Sep 21, 2018

    Currently the watershed tool in Spatial Analyst will default the extent to the intersection of inputs, which is almost always the pour point layer.  That results in watersheds are truncated because of the spatial extent of the output raster.  It should almost always default the other way around, to the flow direction raster or use union of inputs so that watersheds don't get chopped off.  I propose that for this tool that the defaults are set to override the normal defaults.