Don't double count selected entity weight when on building.

megamek/src/megamek/common/ConstructionFactorWarning.java

@@ -187,7 +187,9 @@ protected static double calculateTotalTonnage(Game g, Entity e, Coords c) {
 		double totalWeight = e.getWeight();
 		List<Entity> units = g.getEntitiesVector(c, true);
 		for (Entity ent : units) {
-			totalWeight += ent.getWeight();
+			if (e != ent) {
+				totalWeight += ent.getWeight();
+			}
 		}
 		return totalWeight;
 	}

megamek/unittests/megamek/common/ConstructionFactorWarningTest.java

@@ -328,6 +328,27 @@ public void testConstructionFactorWarningCalcTotalWeightWithUnit() {
 		assertEquals(entityWeight + onBuildingWeight, totalWeight);
 	}
 
+	@Test
+	public void testConstructionFactorWarningCalcTotalWeightEntityOnBuilding() {
+		// This test simulates the selected entity on a building.  When
+		// calculating the weight we don't want to double count ourselves. (we
+		// are already accounting for our own weigh as the selected entity)
+		double entityWeight = 35.0;
+
+		Game g = mock(Game.class);
+		Entity e = createMockEntityWith(new Coords(3, 3), 5, 3, entityWeight, true, false);
+
+		// Mock a 25 ton entity already on the building hex.
+		List<Entity> entities = new ArrayList<Entity>();
+		entities.add(e);
+
+		when(g.getEntitiesVector(new Coords(3, 3), true)).thenReturn(entities);
+
+		double totalWeight = ConstructionFactorWarning.calculateTotalTonnage(g, e, new Coords(3,3));
+
+		assertEquals(entityWeight, totalWeight);
+	}
+
 	// Helper function to setup a mock entity with various attributes.
 	private Entity createMockEntityWith(Coords pos, int run, int jump, double weight, boolean ground, boolean offboard) {
 		Entity e = mock(Entity.class);