Added QRCode generation functions via libqrencode. Switch on with USE_QRENCODE=1.

Amended build docs for Linux and OSX, and OSX makefile.
Added package 'qrencode' to gitian.yml

src/qt/addressbookpage.cpp

@@ -10,6 +10,10 @@
 #include <QFileDialog>
 #include <QMessageBox>
 
+#ifdef USE_QRCODE
+#include "qrcodedialog.h"
+#endif
+
 AddressBookPage::AddressBookPage(Mode mode, Tabs tab, QWidget *parent) :
     QDialog(parent),
     ui(new Ui::AddressBookPage),
@@ -25,6 +29,10 @@ AddressBookPage::AddressBookPage(Mode mode, Tabs tab, QWidget *parent) :
     ui->deleteButton->setIcon(QIcon());
 #endif
 
+#ifndef USE_QRCODE
+    ui->showQRCode->setVisible(false);
+#endif
+
     switch(mode)
     {
     case ForSending:
@@ -169,10 +177,12 @@ void AddressBookPage::selectionChanged()
             break;
         }
         ui->copyToClipboard->setEnabled(true);
+        ui->showQRCode->setEnabled(true);
     }
     else
     {
         ui->deleteButton->setEnabled(false);
+        ui->showQRCode->setEnabled(false);
         ui->copyToClipboard->setEnabled(false);
     }
 }
@@ -227,3 +237,23 @@ void AddressBookPage::exportClicked()
                               QMessageBox::Abort, QMessageBox::Abort);
     }
 }
+
+void AddressBookPage::on_showQRCode_clicked()
+{
+#ifdef USE_QRCODE
+    QTableView *table = ui->tableView;
+    QModelIndexList indexes = table->selectionModel()->selectedRows(AddressTableModel::Address);
+
+
+    QRCodeDialog *d;
+    foreach (QModelIndex index, indexes)
+    {
+        QString address = index.data().toString(),
+            label = index.sibling(index.row(), 0).data().toString(),
+            title = QString("%1 << %2 >>").arg(label).arg(address);
+
+        QRCodeDialog *d = new QRCodeDialog(title, address, label, tab == ReceivingTab, this);
+        d->show();
+    }
+#endif
+}