add DebugLocks build flag

Using the method described in
https://www.fpcomplete.com/blog/2018/05/pinpointing-deadlocks-in-haskell
but my own code to implement it, and with callstacks added.

This work is supported by the NIH-funded NICEMAN (ReproNim TR&D3) project.

Annex/Ssh.hs

@@ -198,7 +198,7 @@ prepSocket socketfile sshhost sshparams = do
 	-- When the LockCache already has the socketlock in it,
 	-- the connection has already been started. Otherwise,
 	-- get the connection started now.
-	makeconnection socketlock =
+	makeconnection socketlock = debugLocks $
 		whenM (isNothing <$> fromLockCache socketlock) $
 			-- See if ssh can connect in batch mode,
 			-- if so there's no need to block for a password