Issue in multiline xAxis label positioning when using axis.x.rotate

When loading new data, the xAxis label is badly positioned when using rotate option.

See http://jsfiddle.net/m9c8qpd2/

The issue is here:

```
AxisInternal.prototype.updateTickTextCharSize = function (tick) {
var internal = this;
if (internal.tickTextCharSize) {
return internal.tickTextCharSize;
}
var size = {
h: 11.5,
w: 5.5
};
tick.select('text').text(function(d) { return internal.textFormatted(d); }).each(function (d) {
var box = this.getBoundingClientRect(),
text = internal.textFormatted(d),
h = box.height,
w = text ? (box.width / text.length) : undefined;
if (h && w) {
size.h = h;
size.w = w;
}
}).text('');
internal.tickTextCharSize = size;
return size;
};
```

We are recomputing the "text char size" using the box's height whereas this is false when the box is rotated.