commit new transaction after 60 seconds

Database.Handle can now be given a CommitPolicy, making it easy to specify
transaction granularity.

Benchmarking the old git-annex incremental fsck that flips sticky bits
to the new that uses sqlite, running in a repo with 37000 annexed files,
both from cold cache:

old: 6m6.906s
new: 6m26.913s

This commit was sponsored by TasLUG.

Command/Fsck.hs

@@ -443,9 +443,7 @@ withFsckDb (StartIncremental h) a = a h
 withFsckDb NonIncremental _ = noop
 
 recordFsckTime :: Incremental -> Key -> Annex ()
-recordFsckTime inc key = withFsckDb inc $ \h -> liftIO $ do
-	FsckDb.addDb h key
-	FsckDb.commitDb h
+recordFsckTime inc key = withFsckDb inc $ \h -> liftIO $ FsckDb.addDb h key
 
 {- Records the start time of an incremental fsck.
  -