Added test for implicit union of render() children

testdata/scad/features/render-2d-tests.scad

@@ -1,6 +1,11 @@
 render() {
   difference() {
-    square(100, center=true);
-    circle(r=30);
+    square(10, center=true);
+    circle(r=3);
   }
 }
+
+translate([12,0,0]) render() {
+  square(10, center=true);
+  circle(r=3);
+}

tests/regression/dumptest/render-2d-tests-expected.csg

@@ -1,8 +1,14 @@
 group() {
 	render(convexity = 1) {
 		difference() {
-			square(size = [100, 100], center = true);
-			circle($fn = 0, $fa = 12, $fs = 2, r = 30);
+			square(size = [10, 10], center = true);
+			circle($fn = 0, $fa = 12, $fs = 2, r = 3);
+		}
+	}
+	multmatrix([[1, 0, 0, 12], [0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 1]]) {
+		render(convexity = 1) {
+			square(size = [10, 10], center = true);
+			circle($fn = 0, $fa = 12, $fs = 2, r = 3);
 		}
 	}
 }