Data.Map.toDescList not exported?

[Evan Laforge]

It's in the source, marked as being O(n), but it's not in the export
list.  Oversight?  I'm using ghc-6.8.2.

I'm using (reverse.toAscList) but I think running 'head' on that is
going to be less efficient than on the real toDescList.

Thanks!