Adding "deselected_node" attribute to "event" object of "tree.select" event

Hi,

I found, that while of "tree.select" event's progress one can't to access to the node, that was selected before current node (that selecting catched by this event). But this object I need in commercial web-project very much (and I'm absolutely sure that this feature will help some peoples, which need to do something with deselected node).

I just added attribute, compiled all coffee-files into generally js-file (that on root) and wrote separate test for this behavior.

It's my first pull request, so sorry for possible errors or my not yes fluent english skills :)

P.S.: I use your plugin in RubyOnRails web-app.