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.
To get IE7 support, the OpenLayers.Format.JSON parser should be used. This leverages the native JSON.parse method where available. It does add extra weight to UTFGrid builds. However, as of this commit date, we lose large portions of US govt agencies when we exclude IE7.
I would think there would still be an error thrown here. Will put together a test to determine for sure, but I'd think that the default GeoJSON parser used by the protocol would choke on the UTFGrid json.
