Nested C class setters restored in c++out mode for Octave

Suitable casts are required so that assignment of instances of nested classes
work as the nested class is duplicated in the global namespace, eg:

struct Outer {
  struct Nested {
    int bar;
  } bar_instance;
};

Outer.bar_instance can now be assigned to.

Examples/test-suite/nested_structs.i

@@ -23,6 +23,8 @@ void setValues(struct Outer *outer, int val) {
   outer->inside3 = &outer->inside2;
   outer->inside4[0].val = val * 4;
 }
+
+int getInside1Val(struct Outer *n) { return n->inside1.val; }
 %}
 
 /* 

Examples/test-suite/octave/nested_structs_runme.m

@@ -0,0 +1,14 @@
+nested_structs
+
+named = nested_structs.Named();
+named.val = 999;
+assert(nested_structs.nestedByVal(named), 999);
+assert(nested_structs.nestedByPtr(named), 999);
+
+outer = nested_structs.Outer();
+outer.inside1.val = 456;
+assert(nested_structs.getInside1Val(outer), 456);
+
+outer.inside1 = named;
+assert(nested_structs.getInside1Val(outer), 999);
+