Fix filter() function parameter in jquery externs

[fredj]

This PR suggests to fix the signature of the jquery filter parameter; the function callback takes a number and an Element in argument, not only a number.

See http://api.jquery.com/filter/#filter-function

[fredj]

@MatrixFrog CLA already signed: https://github.com/google/closure-compiler/blob/master/CONTRIBUTORS#L43

[MatrixFrog]

Chad/John, did you have any comments on this? I'm pretty sure this won't break anyone because the typechecker treats function(number) as a subtype of function(number, Element) right?

[ChadKillingsworth]

If we are concerned about existing code, we can mark it as

function(number, Element=)

It's a callback function, so the arguments being optional would make sense.

[MatrixFrog]

I'm pretty sure this won't break anyone, and we can rollback if I'm wrong :)