clean up read/show abuse

Avoid ever using read to parse a non-haskell formatted input string.

show :: Key is arguably still show abuse, but displaying Keys as filenames
is just too useful to give up.

Common/Annex.hs

@@ -1,6 +1,7 @@
 module Common.Annex (
 	module Common,
 	module Types,
+	module Types.UUID,
 	module Annex,
 	module Locations,
 	module Messages,
@@ -8,6 +9,7 @@ module Common.Annex (
 
 import Common
 import Types
+import Types.UUID (toUUID, fromUUID)
 import Annex (gitRepo)
 import Locations
 import Messages