Adds ability to disable automatic image dimension application to <img> elements.

[bentruyman]

We're experiencing issues with our responsive design implementation when images have explicit widths are applied to them. This is also an issue when serving 2x images for high-density displays. Typically, we want images to simply take up only the space that they are provided since they'll likely be in a flexible container.

Normally this works fine, but IE8 in particular is having issues with max-width: 100% and height: auto on images that have an explicit width.

This PR allows you to disable that functionality.

[j15e]

The real fix would be to provide an helper named something like asset_path which would return only the url of an asset, not an HTML tag, which would avoid having such setting.

I think what I will do in the end is simply removing the auto image size feature as it will annoy more than help most front-end people, what do you think?

cc @renaudleo @cloutierlp

[bentruyman]

Removing it would also work. It's not much work to re-add the dimensions manually. And with responsive design, you rarely ever specify the dimensions.

[renaudleo]

I agree we should probably just remove it, or at least not make it the default behavior. As @bentruyman said, you now rarely specify dimensions unless you're serving 2x images, which, anyway would not work with the actual behavior.

That being said, an asset_path helper would probably be great too, even if the auto image size attributes is removed.