Function push

src/common/classes/alloc.cpp:207–219

	template <class T>
	void push(T** where, T* e)
	{
		// set element `e' pointers
		e->prev = where;
		e->next = *where;

		// make next after `e' element (if present) point to it
		if (e->next)
			e->next->prev = &(e->next);

		// make previous element point to `e'
		*(e->prev) = e;
	}

	template <class T>
	void remove(T* e)