bars with base autorange bug

[alexcjohnson]

We still include tozero in the autorange for bar traces even if there's a base that means no bars start at 0. For example:

Plotly.newPlot(gd,[{y:[1,2,3],base:[3,4,5],type:'bar'}],{width:400,height:400})

This should instead get a regular padded autorange from 3 to 8.