Make the weak pointer work. Some bits were left when importing.

Modified Files:
	SGSharedPtr.hxx SGWeakPtr.hxx

simgear/structure/SGSharedPtr.hxx

@@ -98,6 +98,8 @@ public:
 private:
   void assign(T* p)
   { get(p); put(); _ptr = p; }
+  void assignNonRef(T* p)
+  { put(); _ptr = p; }
 
   void get(const T* p) const
   { T::get(p); }

simgear/structure/SGWeakPtr.hxx

@@ -27,6 +27,8 @@ public:
   { }
   SGWeakPtr(const SGWeakPtr& p) : mWeakData(p.mWeakData)
   { }
+  SGWeakPtr(T* ptr)
+  { assign(ptr); }
   template<typename U>
   SGWeakPtr(const SGSharedPtr<U>& p)
   { SGSharedPtr<T> sharedPtr = p; assign(sharedPtr.get()); }