use lock pools throughout git-annex

The one exception is in Utility.Daemon. As long as a process only
daemonizes once, which seems reasonable, and as long as it avoids calling
checkDaemon once it's already running as a daemon, the fcntl locking
gotchas won't be a problem there.

Annex.LockFile has it's own separate lock pool layer, which has been
renamed to LockCache. This is a persistent cache of locks that persist
until closed.

This is not quite done; lockContent stil needs to be converted.

Database/Fsck.hs

@@ -74,7 +74,7 @@ openDb u = do
 		liftIO $ do
 			void $ tryIO $ removeDirectoryRecursive dbdir
 			rename tmpdbdir dbdir
-	lockFileShared =<< fromRepo (gitAnnexFsckDbLock u)
+	lockFileCached =<< fromRepo (gitAnnexFsckDbLock u)
 	h <- liftIO $ H.openDb db "fscked"
 	return $ FsckHandle h u