Added test case for parent_module()

testdata/scad/misc/parent_module-tests.scad

@@ -0,0 +1,26 @@
+/*
+	$parent_modules should return the number of module in the module 
+    instantiation stack. The stack is independent on where the modules 
+    are defined. It's where they're instantiated that counts.
+
+    parent_module(N) returns the Nth module name in the stack
+*/
+module print(name) {
+  echo("name: ", name);
+  for (i=[1:$parent_modules-1]) echo(parent_module(i));
+}
+
+module yyy() {
+  print("yyy");
+}
+
+module test() {
+  module xxx() {
+    print("xxx");
+    yyy();
+  }
+  print("test");
+  xxx();
+}
+
+test();