Fix shadow in DisplayStyleDrawer Theme.

When you use DisplayStyleDrawer theme for first time the shadow of masterView is not hidden.



    BDBSplitViewController *splitViewController = [[BDBSplitViewController alloc] initWithMasterViewController:[MasterViewController new]
                                                                                          detailViewController:[[DrawerDetailViewController alloc] initWithNibName:nil bundle:nil]];



Before: 
![screen shot 2014-03-11 at 5 11 01](https://f.cloud.github.com/assets/1813468/2381144/eaa43c9a-a8bb-11e3-9ab2-ac2c3068c20b.png)

After: 
![screen shot 2014-03-11 at 5 24 13](https://f.cloud.github.com/assets/1813468/2381146/f8e2650c-a8bb-11e3-8b51-acc14ccf1ed4.png)