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

[Max Rabkin]

On Fri, Mar 26, 2010 at 6:00 PM, Adam Vogt <vogt.adam at gmail.com> wrote:
> At the time it didn't seem sensible to extend the already sizable class
> without having any code that actually needed the new method.

X.L.Drawer could be made more correct using this (since the modifier
tracks an arbitrary second layout). Currently it assumes that layout
doesn't change, since this method was missing.

--Max