nub transitionList to avoid ugly message after repeated transitions, and avoid redundant work for repeated ForgetDeadRemotes transitions

Annex/Branch.hs

@@ -522,7 +522,7 @@ performTransitionsLocked jl ts neednewlocalbranch transitionedrefs = do
 	Annex.Queue.flush
 	withIndex $ do
 		prepareModifyIndex jl
-		run $ mapMaybe getTransitionCalculator $ transitionList ts
+		run $ mapMaybe getTransitionCalculator tlist
 		Annex.Queue.flush
 		if neednewlocalbranch
 			then do
@@ -535,7 +535,8 @@ performTransitionsLocked jl ts neednewlocalbranch transitionedrefs = do
 	message
 		| neednewlocalbranch && null transitionedrefs = "new branch for transition " ++ tdesc
 		| otherwise = "continuing transition " ++ tdesc
-	tdesc = show $ map describeTransition $ transitionList ts
+	tdesc = show $ map describeTransition tlist
+	tlist = transitionList ts
 
 	{- The changes to make to the branch are calculated and applied to
 	 - the branch directly, rather than going through the journal,

Logs/Transitions.hs

@@ -77,7 +77,7 @@ combineTransitions :: [Transitions] -> Transitions
 combineTransitions = S.unions
 
 transitionList :: Transitions -> [Transition]
-transitionList = map transition . S.elems
+transitionList = nub . map transition . S.elems
 
 {- Typically ran with Annex.Branch.change, but we can't import Annex.Branch
  - here since it depends on this module. -}