Use Control.Exception.catch explitly to avoid warnings

The base that comes with ghc-7.6.1 no longer includes Prelude.catch;
so these modules were changed so that there is no warning for

import Prelude hiding (catch)

At the same time these changes should be compatible with older GHCs,
since the catch being has never been the one in the Prelude.

XMonad/Prompt/Shell.hs

@@ -30,10 +30,9 @@ module XMonad.Prompt.Shell
     ) where
 
 import           Codec.Binary.UTF8.String (encodeString)
-import           Control.Exception
+import           Control.Exception        as E
 import           Control.Monad            (forM)
 import           Data.List                (isPrefixOf)
-import           Prelude                  hiding (catch)
 import           System.Directory         (doesDirectoryExist, getDirectoryContents)
 import           System.Environment       (getEnv)
 import           System.Posix.Files       (getFileStatus, isDirectory)
@@ -111,7 +110,7 @@ commandCompletionFunction cmds str | '/' `elem` str = []
 
 getCommands :: IO [String]
 getCommands = do
-    p  <- getEnv "PATH" `catch` econst []
+    p  <- getEnv "PATH" `E.catch` econst []
     let ds = filter (/= "") $ split ':' p
     es <- forM ds $ \d -> do
         exists <- doesDirectoryExist d
@@ -142,7 +141,7 @@ isSpecialChar =  flip elem " &\\@\"'#?$*()[]{};"
 --   In order to /set/ an environment variable (eg. combine with a prompt so you can modify @$HTTP_PROXY@ dynamically),
 --   you need to use 'System.Posix.putEnv'.
 env :: String -> String -> IO String
-env variable fallthrough = getEnv variable `catch` econst fallthrough
+env variable fallthrough = getEnv variable `E.catch` econst fallthrough
 
 {- | Ask the shell what browser the user likes. If the user hasn't defined any
    $BROWSER, defaults to returning \"firefox\", since that seems to be the most