[xmonad] Change build directory to ~/.cache/xmonad

[wagnerdm at seas.upenn.edu]

Quoting Daniel Trstenjak <daniel.trstenjak at gmail.com>:

>
>> If you look a tad further down the patch list, you'll see it ends in
>> ~/.cache/xmonad, presumably following the XDG spec, which was
>> designed exactly to avoid namespace pollution.
>
> What's the darcs way for cleaning up a set of patches?

There's darcs amend-record, but I don't think it's necessary. This  
history is nicely transparent about how and why each change was made.

~d