Forward req/error with ajax:error event.
Don't overwrite jQuery.elastic when it's already defined

This change allows users to have their own implementation of jQuery.elastic plugin.
Test checkbox with images
Allow checkboxes with images
Merge pull request #208 from jdudek/elastic-no-overwrite

Don't overwrite jQuery.elastic when it's already defined
Merge pull request #210 from guigs/checkbox-with-image

Checkboxes with images
Merge pull request #205 from mikedll/master

Using ajax:error with event arguments.