[xmonad] darcs patch: X.A.TopicSpace: new viewMethod field

I've attached a small patch which adds a 'viewMethod' field to TopicSpace configs, allowing the user to choose what method (usually view or greedyView) is used to view workspaces. This will not break any configs (except for those silly enough to use an explicit TopicConfig constructor instead of overriding fields in the default config record) since the default is the same as the old behavior. -Brent