A growing number of packages don't build with the old version. I was
reluctant to make that change because Haskell Platform 2011.2.0.1 says
that text 0.11.0.6 ought to be used, but then HP says we shouldn't be
using GHC 7.0.4 either, yet we do. Anyway, upgrading the text library
caused no problems: all packages just built fine, so there you go.
svn path=/nixpkgs/trunk/; revision=28923
1392096d69