Rename variables "state" to avoid warnings about shadowing

XMonad core re-exports Control.Monad.State, which includes
a function "state" if you happen to use mtl-2. Since there's
a chance xmonad still works with mtl-1 avoid imports like:

import XMonad hiding (state)

XMonad/Actions/Plane.hs

@@ -110,7 +110,7 @@ plane ::
     (WorkspaceId -> WindowSet -> WindowSet) -> Lines -> Limits -> Direction ->
     X ()
 plane function numberLines_ limits direction = do
-    state <- get
+    st <- get
     xconf <- ask
 
     numberLines <-
@@ -205,7 +205,7 @@ plane function numberLines_ limits direction = do
         preColumns = div areas numberLines
 
         mCurrentWS :: Maybe Int
-        mCurrentWS = elemIndex (currentTag $ windowset state) areaNames
+        mCurrentWS = elemIndex (currentTag $ windowset st) areaNames
 
         areas :: Int
         areas = length areaNames