Areal weighing test completed with buggy code

[fnorf]

npm test did not show errors for areal-weighting when I accidentally returned the whole sourceFeatures list from getIntersectingFeatures instead of only the filtered sourceList.

  sourceList = sourceFeatures;
  return [sourceList, intersects];

cogran -d -i testdata/berlin/kriminalitaet_bezirksregionen.geojson -t testdata/berlin/447_lor_planungsraeume.geojson -o testdata/berlin/arealWeighting_kriminalitaet_bezirksregionenToPlanungsraeume.geojson --attr Alle_2012 returned totally wrong values for Alle_2012 then though, as to be expected.

To reproduce add this in line 47 of https://github.com/berlinermorgenpost/cogran/blob/master/lib/methods/areal-weighting.js#L47:
sourceList = sourceFeatures;

Areal weighing testing might need some more cases.