imageOverlay not supported

Nobody has claimed this yet.

I tried adding imageoverlay, but it doesn't seem right. Any help? Thx!
CC: @jieter

``` lang=javascript
function drawTileLayer(l) {
if (l instanceof L.TileLayer) layerQueue.defer(handleTileLayer, l);
else if (l instanceof L.ImageOverlay) layerQueue.defer(handleImageOverlay, l);
else if (l._heat) layerQueue.defer(handlePathRoot, l._canvas);
}
...
function handleImageOverlay(imgOverlay, callback) {
var imgBounds = imgOverlay.getBounds(),
bounds = new L.Bounds(
map.latLngToLayerPoint(imgBounds.getNorthWest()),
map.latLngToLayerPoint(imgBounds.getSouthEast())),
size = bounds.getSize();
var ctx = canvas.getContext('2d');
ctx.drawImage(imgOverlay._url, bounds.min.x, bounds.min.y, size.x, size.y);
callback(null, { canvas: canvas });
}
```

Start with drawTileLayer and handleImageOverlay in the issue example, then compare the ImageOverlay path with the existing TileLayer handling. Determine what is wrong with the current image-overlay rendering and verify that an overlay appears correctly in the generated image.

Written by the indexing model from the issue text.