proxying GET now working

Memory use is small and constant; receiveBytes returns a lazy bytestring
and it does stream.

Comparing speed of a get of a 500 mb file over proxy from origin-origin,
vs from the same remote over a direct ssh:

joey@darkstar:~/tmp/bench/client>/usr/bin/time git-annex get bigfile --from origin-origin
get bigfile (from origin-origin...)
ok
(recording state in git...)
1.89user 0.67system 0:10.79elapsed 23%CPU (0avgtext+0avgdata 68716maxresident)k
0inputs+984320outputs (0major+10779minor)pagefaults 0swaps

joey@darkstar:~/tmp/bench/client>/usr/bin/time git-annex get bigfile --from direct-ssh
get bigfile (from direct-ssh...)
ok
1.79user 0.63system 0:10.49elapsed 23%CPU (0avgtext+0avgdata 65776maxresident)k
0inputs+1024312outputs (0major+9773minor)pagefaults 0swaps

So the proxy doesn't add much overhead even when run on the same machine as
the client and remote.

Still, piping receiveBytes into sendBytes like this does suggest that the proxy
could be made to use less CPU resouces by using `sendfile()`.

Annex/UUID.hs

@@ -79,7 +79,6 @@ getRepoUUID r = do
 	
 	if c /= u && u /= NoUUID
 		then do
-			liftIO $ print (r, "setting cache", c, u)
 			updatecache u
 			return u
 		else return c