Make arctan2 work with ScalarQuantities

Ensures that x and y use the same unit, which is otherwise ignored (it is divided out).

Author: rieder

src/amuse/units/trigo.py

@@ -9,7 +9,10 @@
 arcsin = lambda x: numpy.arcsin(x) | rad
 arccos = lambda x: numpy.arccos(x) | rad
 arctan = lambda x: numpy.arctan(x) | rad
-arctan2 = lambda x, y: numpy.arctan2(x, y) | rad
+arctan2 = lambda x, y: numpy.arctan2(
+    x.value_in(x.unit),
+    y.value_in(x.unit),
+) | rad
 
 
 def to_rad(angle):