Previously, Bing overlays that were added to an existing map had empty tiles, because tiles are added before the layer url is set in initLayer. This change makes sure tiles are only rendered when the layer url is available, by not processing the tile queue before the layer url is set.
The tileQueue might have entries again after zooming when the previous zoom level hasn't finished loading yet. Removing the check for the tileQueue's length makes layers report loadend correctly again.
layer.maxExtent is always set as soon as the layer is added to a map. Instead, making behavior consistent with tiled layers: don't display outside maxExtent except when displayOutsideMaxExtent is set to true or the layer's extent equals the world bounds for maps with a baseLayer that has wrapDateLine set to true.
The UTFGrid layer's `getTileInfo` method was not correctly handling dateline wrapping (and was a bit more complicated than it needed to be). Since it would be useful to all grid layers to be able to retrieve a tile and pixel offset for any map location, this functionality deserves to be on the Grid layer.
The WMTS layer currently exposes a `getTileInfo` method that is used within the layer and by the WMTSGetFeatureInfo control. This method could be renamed to `getRemoteTileInfo` or something to differentiate it from a method that gets locally cached tile info. Until that change is made, the method on the Grid layer will be called `getGridData`.
For this to be useful (i.e. so listeners can see/modify the tile url), a change in Tile.Image is required so we do not fire the loadstart event before we have the url to load.
Having to call two methods to get complete feature information (id and data) is cumbersome. The `getFeatureInfo` method returns an object with both feature id and data.
The tile now has responsibility for resolving feature ids and fetching feature data given x, y pixel offsets with getFeatureId and getFeatureData methods. The layer has corresponding getFeatureId and getFeatureData methods that take a map location, lookup the appropriate tile, and delegate to the tile for the rest of the work.
