Adds the new option 'heightIgnoreClass' to manage more complex layout…

[moonClimber]

… (with other elements between current scroll element and its parent)

it would be useful to integrate this new option to manage more complex layout.
Here is my case

<div id="mainContainer">
  <div id="otherElement1" class="listScrollIgnore">any content...</div>
  <div id="otherElement2" class="listScrollIgnore">any content...</div>
  <div id="elementToScroll" class="listScrollIgnore">my list</div>
</div>

By calling

$('#elementToScroll').slimScroll({
        height:'auto',
        heightIgnoreClass: 'listScrollIgnore'
    });

everything works fine since the outerHeights of otherElement1 and otherElement2 are ignored.