MousePosition example issues

See http://ol3js.org/en/master/examples/mouse-position.html

In Firefox 24 (Ubuntu Linux):
* Entering a number in the precision field results in `NaN` being displayed in the field and the precision being interpretted as `0` (only integer coordinates)

In Chrome 30 (Ubuntu Linux);
* Using the arrow up on the precision-numberfield (e.g. to `5`) will lead to to only integer coordinates
* If you enter `0` manually directly afterwards in the field and hover again, you get 5 digits after the comma for the coordinates
* Increasing / decreasing now always show the value previously entered

See also #1186