@Override
	public E remove(int index) {
		checkIndex(index);
		return doRemove(index);
	}
Helper method for adding an element to the list.
This is the only method which really adds an element.
Override if you need to validity checks before adding.

@param index	index where element should be added
             (-1 means it is up to the implementation to choose the index)
@param elem	element to add
@return      true if element has been added, false otherwise
jphp-runtime/src/php/runtime/memory/support/IList.java