Return a bool to indicate whether PullPaymentBid.bid() is successful.

contracts/examples/PullPaymentBid.sol

@@ -4,13 +4,14 @@ contract PullPaymentBid is PullPaymentCapable {
   address public highestBidder;
   uint public highestBid;
 
-  function bid() external {
-    if (msg.value <= highestBid) throw;
+  function bid() external returns (bool) {
+    if (msg.value <= highestBid) return false;
 
     if (highestBidder != 0) {
       asyncSend(highestBidder, highestBid);
     }
     highestBidder = msg.sender;
     highestBid = msg.value;
+    return true;
   }
 }