Payment Protocol: X509-validated payment requests

Add support for a Payment Protocol to Bitcoin-Qt.

Payment messages are protocol-buffer encoded and communicated over
http(s), so this adds a dependency on the Google protocol buffer
library, and requires Qt with OpenSSL support.

src/qt/paymentrequestplus.h

@@ -0,0 +1,41 @@
+#ifndef PAYMENTREQUESTPLUS_H
+#define PAYMENTREQUESTPLUS_H
+
+#include <QByteArray>
+#include <QList>
+#include <QString>
+
+#include "base58.h"
+#include "paymentrequest.pb.h"
+
+//
+// Wraps dumb protocol buffer paymentRequest
+// with extra methods
+//
+
+class PaymentRequestPlus
+{
+public:
+    PaymentRequestPlus() { }
+
+    bool parse(const QByteArray& data);
+    bool SerializeToString(string* output) const;
+
+    bool IsInitialized() const;
+    QString getPKIType() const;
+    // Returns true if merchant's identity is authenticated, and
+    // returns human-readable merchant identity in merchant
+    bool getMerchant(X509_STORE* certStore, QString& merchant) const;
+
+    // Returns list of outputs, amount
+    QList<std::pair<CScript,qint64> > getPayTo() const;
+
+    const payments::PaymentDetails& getDetails() const { return details; }
+
+private:
+    payments::PaymentRequest paymentRequest;
+    payments::PaymentDetails details;
+};
+
+#endif // PAYMENTREQUESTPLUS_H
+