Dashboard: set two columns as default for IE8 (as it doesn't support @media rules), see #25824.

git-svn-id: https://develop.svn.wordpress.org/trunk@26784 602fd350-edb4-49c9-b593-d223f7449a82
Fake a "non-responsive" window width for IE < 9 when folding/unfolding the menu (old IE doesn't support @media), fixes #26458.

git-svn-id: https://develop.svn.wordpress.org/trunk@26785 602fd350-edb4-49c9-b593-d223f7449a82