propagate signals to the transferrer process group

Done on unix, could not implement it on windows quite.

The signal library gets part of the way needed for windows.
But I had to open https://github.com/pmlodawski/signal/issues/1 because
it lacks raiseSignal.

Also, I don't know what the equivilant of getProcessGroupIDOf is on
windows. And System.Process does not provide a way to send any signal to
a process group except for SIGINT.

This commit was sponsored by Boyd Stephen Smith Jr. on Patreon.

Command/Fsck.hs

@@ -662,7 +662,7 @@ cleanupIncremental _ = return ()
 openFsckDb :: UUID -> Annex FsckDb.FsckHandle
 openFsckDb u = do
 	h <- FsckDb.openDb u
-	Annex.addCleanup FsckCleanup $
+	Annex.addCleanupAction FsckCleanup $
 		FsckDb.closeDb h
 	return h