Make task columns display correctly on IE7.

See bug for details:
https://bugzilla.wikimedia.org/show_bug.cgi?id=45527

Solution description:
http://mathiasbynens.be/notes/safe-css-hacks#css-hacks
http://stackoverflow.com/a/5838575

Bug: 45527
Change-Id: I8e5979f1dcc184cd5a8a478a32f5c0420f1d8d00
Merge "Make task columns display correctly on IE7."