JQuery :: How To Abort Fadein / Out Processing

This is my first time using jquery and Ive designed a small and simple fadein/out script that acts as a rollover on this navigation bar: [URL] Here is the code:

$(document).ready(function() {
$(".navbutton").not("#active").hover(function(){
$(this).siblings(".rollover").fadeIn(300);
},function(){
$(this).siblings(".rollover").fadeOut(300);
});
});

It works great. However, if a user quickly moves their mouse over the nav buttons and repeats the process, the rollover affect will fadein/ out over and over again until its completed the cycle the amount of times the user moved the mouse over the button back and forth. I wish to change this behaviour so that, somehow, the processing is aborted if it is noticed the mouse is not present after a fadeout is completed.