added one method to get cross-domain script.

[LeoYuan]

see the following issues please.
#607
#609
#610

[imaffett]

Hey @LeoYuan

I was always confused by the PR you added for $().data and JSON. $().attr() already handles taking in an object and storing it. I think what you were doing was passing in a string and wanting an object back right?

[LeoYuan]

issue #607
yes, I just copied the code fragment from jQuery, if you don't think this is a good way, I can write a version of my own, quite simple.

issue #609
I may not make things clear, just run the sample code in #609, you will get what I mean.

issue #610
same as the above one, just run the code, an error will be thrown.
dive into the code, you will find the code in function attr()/prop() is not robust enough when you decide to use a _propCache/_attrCache object.

[imaffett]

Can you please write your own version? There are legal issues about using code from other projects.

I believe #609 and #610 are fixed in 2.1 in different - everything is now in attr().