Add a SplitPullPayment contract that combines distribution of funds and delayed withdrawal from each party

contracts/payment/SplitPullPayment.sol

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+pragma solidity ^0.4.15;
+
+import './PullPayment.sol';
+import './SplitPayment.sol';
+
+/**
+ * @title SplitPullPayment
+ * @dev Contract supporting the distribution of funds combined with withdrawals through PullPayment.
+ */
+contract SplitPullPayment is SplitPayment, PullPayment {
+  /**
+   * @dev Return the total amount of funds available for distribution. 
+   * @dev Override from SplitPayment to take into account credited funds for pull payments.
+   */
+  function toDistribute() internal returns (uint256) {
+    return this.balance.sub(totalPayments);
+  }
+
+  /**
+   * @dev Perform the payment to a payee. 
+   * @dev Override from SplitPayment to do an asyncSend for later withdrawal.
+   * @param _payee The address of the payee to be paid.
+   * @param _amount The amount for the payment.
+   */
+  function pay(address _payee, uint256 _amount) internal {
+    asyncSend(_payee, _amount);
+  }
+}