Tooltip: apply position class before positioning

A follow up on this request: https://github.com/twitter/bootstrap/pull/6703
This wasn't fixed with the big push and is still there now, so I wrote a test to go with it.
I haven't figured out a better way to test this, but this one does test things correctly. And also, again, the fix is simply moving a line up.
Another jsbin to illustrate the problem: http://jsbin.com/esuwuj/5/edit

Thanks!! Have a nice day!!!