Fixing getManagerForEl when root element is provided

[fcamblor]

When root collection item element is provided to getManagerForEl(), manager is not resolved because of a missing self-check.

Provided a unit test demonstrating the issue.

Note that I re-generated minified version of Backbone.CollectionBinder.js using https://jscompress.com which makes some variable naming changing in the resulting code.

Tell me if :

• Such minification should not be part of the PR (could be generated at release time)
• I should use another tool to limit the differences compared to existing minified js file