Use global jQuery in this.actual instance check

Here's the thing.

I spent at leat evening with that case. I have two jQuery scripts on the same page. They go in following order:
```
tests/jquery-1.9.1.js
tests/jasmine-jquery.js
app/jquery-1.9.1.js
specs/testSpec.js
```

So local `$` in jasmine-jquery is first script instance, but in specs I got second instance. I know that I doing it wrong, because there may be different jQuery versions, but I think that using global `$` only in instance check it is convenient compromise. Moreover, in `addEqualityTester` you have `a instanceof jQuery` rather than `a instanceof $`, so you should choose only one way.