fix default suffixes in save dialog in GNOME, make it more clear that PNG is used (solves #833)

src/qt/addressbookpage.cpp

@@ -9,7 +9,6 @@
 
 #include <QSortFilterProxyModel>
 #include <QClipboard>
-#include <QFileDialog>
 #include <QMessageBox>
 #include <QMenu>
 
@@ -277,10 +276,9 @@ void AddressBookPage::done(int retval)
 void AddressBookPage::exportClicked()
 {
     // CSV is currently the only supported format
-    QString filename = QFileDialog::getSaveFileName(
+    QString filename = GUIUtil::getSaveFileName(
             this,
-            tr("Export Address Book Data"),
-            QDir::currentPath(),
+            tr("Export Address Book Data"), QString(),
             tr("Comma separated file (*.csv)"));
 
     if (filename.isNull()) return;