Repository tuning parameters can now be passed when initializing a repository for the first time.

* init: Repository tuning parameters can now be passed when initializing a
  repository for the first time. For details, see
  http://git-annex.branchable.com/tuning/
* merge: Refuse to merge changes from a git-annex branch of a repo
  that has been tuned in incompatable ways.

Logs.hs

@@ -39,6 +39,7 @@ topLevelUUIDBasedLogs =
 	, preferredContentLog
 	, requiredContentLog
 	, scheduleLog
+	, differenceLog
 	]
 
 {- All the ways to get a key from a presence log file -}
@@ -82,6 +83,9 @@ groupPreferredContentLog = "group-preferred-content.log"
 scheduleLog :: FilePath
 scheduleLog = "schedule.log"
 
+differenceLog :: FilePath
+differenceLog = "difference.log"
+
 {- The pathname of the location log file for a given key. -}
 locationLogFile :: Key -> String
 locationLogFile key = hashDirLower key ++ keyFile key ++ ".log"