Sped up query commands that read the git-annex branch by around 5%

The only price paid is one additional MVar read per write to the journal.
Presumably writing a journal file dominiates over a MVar read time by
several orders of magnitude.

--batch does not get the speedup because then it needs to notice when
another process has made a change. Also made the assistant and other damon
modes bypass the optimisation, which would not help them anyway.

Types/BranchState.hs

@@ -8,9 +8,17 @@
 module Types.BranchState where
 
 data BranchState = BranchState
-	{ branchUpdated :: Bool -- has the branch been updated this run?
-	, indexChecked :: Bool -- has the index file been checked to exist?
+	{ branchUpdated :: Bool
+	-- ^ has the branch been updated this run?
+	, indexChecked :: Bool
+	-- ^ has the index file been checked to exist?
+	, journalIgnorable :: Bool
+	-- ^ can reading the journal be skipped, while still getting
+	-- sufficiently up-to-date information from the branch?
+	, journalNeverIgnorable :: Bool
+	-- ^ should the journal always be read even if it would normally
+	-- be safe to skip it?
 	}
 
 startBranchState :: BranchState
-startBranchState = BranchState False False
+startBranchState = BranchState False False False False