max-width: 100% on images breaks avatar cropping

[boonebgorges]

I've come across a number of themes that are using the following CSS to help make images more responsive:

img { max-width: 100%; height: auto; }

Setting a max-width on all images has a tendency to break our implementation of jcrop, however, by throwing all images out of proportion, layering images in a weird way, and other such garbage.

I've attached a patch with my suggested fix, which works well on every theme I've tried it with, and seems to be specific enough not to cause any more problems. I'm posting here before committing, though, because I want someone more familiar with responsive techniques to have a look first. In particular, what will this do to the avatar cropper on small devices?

(In [6620]) Force max-width: none; on more jcrop img elements. Props boonebgorges. Fixes #4708.