[xmonad] darcs patch: Add a way to update the modifier in X.L.LayoutModifier

[Adam Vogt]

* On Monday, March 29 2010, Gwern Branwen wrote:

...
>
>Would there be any specific downside to this, though? If X.L.Drawer
>could use this, and there's no downside, there would seem to be a
>benefit to applying.
>
>-- 
>gwern

Correct. While there there is a cost of an additional method for new
developers when trying to understand how to write an instance of
LayoutModifier, I think it is justified if we have _some_ code that uses
those methods.

--
Adam