[xmonad] adding an existing workspace with DynamicWorkspaces?

[Brent Yorgey]

Hi all,

Today, while helping crhalpin in #xmonad, I discovered that if you
call X.A.DynamicWorkspaces.addWorkspace with the name of an
already-existing workspace, it simply makes another one, which
seems... odd.  Does anyone actually rely on this behavior?  Or is it
OK if I fix it so that calling addWorkspace with the name of a
workspace that already exists is a no-op?

-Brent