Sortable: cache original DOM position using all node types

[m-orchard]

Fixes #10800 - Sortable: Cancelling a sort does not return the item to its original position with regard to non-element nodes by caching the original DOM position using previousSibling rather than prev, so all nodes are considered, not just elements.

Here's the original JSFiddle showing the bug:
http://jsfiddle.net/morchard/pups17xL/

And here's a JSFiddle showing the patch:
http://jsfiddle.net/morchard/z60ox3so/

[scottgonzalez]

Closing due to the ticket being closed. jQuery UI is not supposed to drop down to this level.

[m-orchard]

Ah, sorry about this, I didn't spot the existing issue.