Actual value of ignoreLeaks from configuration

`ignoreLeaks` value is ignored by the setup function.

By doing this
````js
mocha.setup({
   ui : "bdd",
   ignoreLeaks : false
});
````
`ignoreLeaks` happens to be `true`.


It happens because the [boot code](https://github.com/visionmedia/mocha/blob/master/support/tail.js#L90)
````js
mocha.setup = function(opts){
    if ('string' == typeof opts) opts = { ui: opts };
    for (var opt in opts) this[opt](opts[opt]);   // calls this.ignoreLeaks(false);
    return this;
};
````
passes the configured value to [this function](https://github.com/visionmedia/mocha/blob/master/lib/mocha.js#L216)
````js
Mocha.prototype.ignoreLeaks = function(){
  this.options.ignoreLeaks = true;
  return this;
};
````
which simply sets the value to `true` no matter what was passed.



I'm not sure how to test this with your suite, probably by appending a 
````js
--ignoreLeaks false
````
in [mocha.opts](https://github.com/visionmedia/mocha/blob/master/test/mocha.opts)