bug fix for collapsed tree panel, which is still visible behind the tab panel

git-svn-id: http://www.pimcore.org/svn/pimcore/private/core/trunk@3057 1f8fe7d8-47f0-464c-8d0a-336f4953ab05
build auto version ...

git-svn-id: http://www.pimcore.org/svn/pimcore/private/core/trunk@3058 1f8fe7d8-47f0-464c-8d0a-336f4953ab05