tested via closure compiler -- removing STR_ON and adding "on" to the strings it was being concatenated to reduces the overall file size slightly.

(As a side effect, the code is simpler to read)

Allow the plugin to be loaded as an AMD module.  For more details, see:
http://requirejs.org/docs/whyamd.html

As a side effect, this prevents things from being instantiated multiple times if the script is included more than once on the page.

Also fire complete callback on abort to give similar behavior to jQuery's $.ajax complete / always

I think it will save 4 bytes after minification, and it's more readable.

Conflicts:
	src/jquery.jsonp.js

Conflicts:
	src/jquery.jsonp.js

…out of the box.