rename PullPaymentCapable=>PullPayment

contracts/test-helpers/PullPaymentMock.sol

@@ -0,0 +1,9 @@
+import '../PullPayment.sol';
+
+// mock class using PullPayment
+contract PullPaymentMock is PullPayment {
+  // test helper function to call asyncSend
+  function callSend(address dest, uint amount) external {
+    asyncSend(dest, amount);
+  }
+}