Change the capacity of this deque such that, after this method returns, iterators remain valid provided that no more than the specified numElements objects are pushed to the front or back of the deque after this call. If it is already possible to push numElements objects to either end of this deque without invalidating iterators, this method has no effect. Note that inserting elements into the deque may still incur memory allocation. Also note that this method, if it has any effect, will invalidate iterators initialized prior to the call. Also note that this method is not part of the C++ standard.