containerResize and slideResize do not work consistently

[ucavus]

It appears that the these options now fail intermittently depending on whether images in the slide have loaded or not. It seems that each slide's height is calculated once at the beginning rather than each time it's shown which can break a slideshow if even one image is missing a dimension attribute and not loaded yet. It seems to be especially bad in webkit-based browsers. I can understand there's a performance hit of doing this, but surely it's not too taxing to query a single slide's width & height. Wouldn't this ensure correct display also enable slides to be added/removed?