Reset: allow re-init of Nasal Ghosts.

After discussion with Thomas, reset needs the scenario this assert
was designed to guard against, so removing it for now.

simgear/nasal/cppbind/Ghost.hxx

@@ -291,8 +291,6 @@ namespace nasal
        */
       static Ghost& init(const std::string& name)
       {
-        assert( !getSingletonPtr() );
-
         getSingletonHolder().reset( new Ghost(name) );
         return *getSingletonPtr();
       }