implemented git-annex-shell p2pstdio

Not yet used by git-annex, but this will allow faster transfers etc than
using individual ssh connections and rsync.

Not called git-annex-shell p2p, because git-annex p2p does something
else and I don't want two subcommands with the same name between the two
for sanity reasons.

This commit was sponsored by Øyvind Andersen Holm.

P2P/IO.hs

@@ -10,6 +10,7 @@
 module P2P.IO
 	( RunProto
 	, P2PConnection(..)
+	, stdioP2PConnection
 	, connectPeer
 	, closeConnection
 	, serveUnixSocket
@@ -50,6 +51,15 @@ data P2PConnection = P2PConnection
 	, connOhdl :: Handle
 	}
 
+-- P2PConnection using stdio.
+stdioP2PConnection :: Git.Repo -> P2PConnection
+stdioP2PConnection g = P2PConnection
+	{ connRepo = g
+	, connCheckAuth = const False
+	, connIhdl = stdin
+	, connOhdl = stdout
+	}
+
 -- Opens a connection to a peer. Does not authenticate with it.
 connectPeer :: Git.Repo -> P2PAddress -> IO P2PConnection
 connectPeer g (TorAnnex onionaddress onionport) = do