Avoid touching the geolocation object until needed

IE9 leaks when `navigator.geolocation` is accessed (see #461).  The goal of this change is to avoid that leak in builds that include the Geolocate control but do not use it.
Merge pull request #461 from tschaub/ie9-leaks

OpenLayers-2.12-rc2 + jQuery-1.7.2 Memory leak in Internet Explorer 9 (p=@tschaub,r=@marcjansen,@elemoine)