String move() and String(String &&rval) breaks operation of reserve()

When #if __cplusplus >= 201103L || defined(__GXX_EXPERIMENTAL_CXX0X__)
operator = uses move() to just update the buffer pointer of the destination
This ignores any reserve() the user has made to ensure the memory is not unnecessarily fragmented.
String(String &&rval) has a similar problem

move() should first check the capacity of the destination and if there is sufficient space copy the source to the destination
String(String &&rval) should use move()

A suggested move() is

```
void String::move(String &rhs) {
if (this != &rhs) {
if (capacity > rhs.size) {
copy(rhs.buffer,rhs.size);
} else {
free(buffer);
buffer = rhs.buffer;
len = rhs.len;
capacity = rhs.capacity;
}
rhs.buffer = NULL;
rhs.len = 0;
rhs.capacity = 0;
}
}
```

Localiza la implementación de String de C++11 e inspecciona move(), operator=, el constructor String(String &&rval) y el comportamiento de reserve(). Verifica cómo se comporta un destino con reserva durante un movimiento y, a continuación, confirma que el constructor sigue la ruta de movimiento prevista y que los strings movidos permanecen en un estado válido.

Escrito por el modelo de indexación a partir del texto del issue.