Adding array diff utility function

[bermi]

I've ported PHP function array_diff to JQuery.

It compares two or more arrays, and returns an array with the values from the first array, only if the value is not present in the second array.

$.diff( ['a','b','c'], ['b','d','e'] );

produces

['a','b']

[john]

Looks good - you should release it as a simple plugin (we currently don't have a need for it in core, and we're being quite selective about what code is currently added).