Fix deadlock in previous implementation

by only allowing new inputs if the previous one has been "acked".

I.e. if you send one diff, you don't process any more diffs until you
	receive a diff back. This is something specified in the Neil Frasier
	paper and also something needed to prevent deadlock.

csp/sync.csp

@@ -11,8 +11,10 @@ empty(patch) = patch == 0
 CLIENT(i, state, shadow) = 
    input!i?new_state
    -> up!i!diff(shadow, new_state)
-   -> CLIENT(i, new_state, shadow)
-[] down!i?patch
+   -> CLIENT'(i, state, shadow)
+[] CLIENT'(i, state, shadow)
+
+CLIENT'(i, state, shadow) = down!i?patch
    -> if empty(patch)
      then CLIENT(i, state, state)
      else 
@@ -25,6 +27,8 @@ CLIENT(i, state, shadow) =
          render!i!apply(state, patch)
          -> CLIENT(i, apply(state, patch), apply(shadow, patch))
 
+
+
 SERVER(i, shadow) = 
    up!i?patch
    -> save!i!patch