Unwrap director classes only when returning a pointer or reference to an object

This involves properly counting the number of references and pointers in the return
type of a function and only generate unwrapping code if this number is 1.
For template instances some post-processing code is added to fix the 'decl' and
'type' attributes of functions if changed in an unfavorable way during template
expansion.
This commit fixes swig#1811.

Examples/test-suite/director_unwrap_result.i

@@ -0,0 +1,82 @@
+%module(directors="1") director_unwrap_result
+
+%warnfilter(SWIGWARN_TYPEMAP_DIRECTOROUT_PTR) Storage;
+%warnfilter(SWIGWARN_TYPEMAP_DIRECTOROUT_PTR) StorageTmpl;
+
+%feature("director") Element;
+%feature("director") Storage;
+%feature("director") StorageTmpl;
+
+%inline %{
+
+class Element {
+  Element* self;
+  Element** selfptr;
+  public:
+    Element() {
+      self = this;
+      selfptr = &self;
+    }
+    virtual ~Element() {}
+    Element **getPtrPtr() {
+      return &self;
+    }
+    Element ***getPtrPtrPtr() {
+      return &selfptr;
+    }
+};
+
+class Storage {
+  public:
+    virtual ~Storage() {}
+    virtual Element **getIt() = 0;
+    Element getElement() {
+      return **getIt();
+    }
+    Element* const getElementPtr() {
+      return *getIt();
+    }
+    Element& getElementRef() {
+      return **getIt();
+    }
+    Element* const *getElementPtrPtr() {
+      return getIt();
+    }
+    Element *&getElementPtrRef() {
+      return *getIt();
+    }
+};
+
+template<class T> class StorageTmpl {
+  public:
+    virtual ~StorageTmpl() {}
+    virtual T &getIt() = 0;
+    T getVal() {
+      return getIt();
+    }
+    T *getPtr() {
+      return &getIt();
+    }
+    T &getRef() {
+      return getIt();
+    }
+};
+
+%}
+
+%template(ElementStorage) StorageTmpl<Element>;
+%template(ElementPtrStorage) StorageTmpl<Element *>;
+%template(ElementPtrPtrStorage) StorageTmpl<Element *const *>;
+
+%inline %{
+
+template<class T> T getParam(T t) {
+  return t;
+}
+
+%}
+
+%template(getIntParam) getParam<int>;
+%template(getIntPtrParam) getParam<int*>;
+%template(getElementPtrParam) getParam<Element *>;
+