Fix IE10 vertical slide perspective

Fixes https://github.com/hakimel/reveal.js/issues/502

IE10 does not support preserve3d see this [IE Dev Center Article](http://msdn.microsoft.com/en-gb/library/ie/hh673529%28v=vs.85%29.aspx#the_ms_transform_style_property)

Here's what the default transition looks like after the fix is applied in IE10: http://youtu.be/g3Pzq7Q2LQo