LPS-29213

http://issues.liferay.com/browse/LPS-29213

Hey Jon,
For this fix, I tested it with various portlets and features to see if any element would overlap Nav submenu.  I did find one element that overlaps in IE7, that does not in other browsers.  That element is the edit `textarea` box for the Quick Note portlet.  To reproduce:
* Run server with CE 6.1.x (Classic _diffs custom.css is different in CE Master)
* Add child pages to a Nav page (E.G. add 7 child pages to "Welcome" page)
* Hit homepage in IE7.  Add Quick Note portlet to top of page
* Click "Click to edit me..." text.
* While `textarea` edit box is open, roll over Nav menu page with child pages.
* My commit will prevent most page elements from overlapping subnav menu, but Quick Note's `textarea` edit box will still overlap

I have tried other portlets and found no other elements which overlap the subnav once my fix is added.  I'm not sure what the solution is for Quick Note overlap.  Quick Note's textarea bounding box, `.aui-editable`, even when changed to `position: relative;` and `z-index: 0;` will still overlap subnav menu.  Likewise, giving `#banner` and all its child nav elements `z-index: 9999;` and giving subnav `ul` the `position: absolute;` still makes no difference.
![LPS-29213](https://f.cloud.github.com/assets/3011386/162805/ed6ee3e8-77d0-11e2-99c9-590c4a6f6ef3.png)