Bitcoin-Qt: BitcoinGUI::message() updates/fixes

- ensure message boxes are shown in center of our main window, not
  centered on the users desktop
- always prefer user supplied titles for message boxes over the functions
  defaults (fixes a bug, where transaction info messages did not contain
  information, if it was incoming or outgoing)

src/qt/bitcoingui.cpp

@@ -590,8 +590,13 @@ void BitcoinGUI::message(const QString &title, const QString &message, unsigned
     int nMBoxIcon = QMessageBox::Information;
     int nNotifyIcon = Notificator::Information;
 
-    // Override title based on style
     QString msgType;
+
+    // Prefer supplied title over style based title
+    if (!title.isEmpty()) {
+        msgType = title;
+    }
+    else {
         switch (style) {
         case CClientUIInterface::MSG_ERROR:
             msgType = tr("Error");
@@ -603,8 +608,10 @@ void BitcoinGUI::message(const QString &title, const QString &message, unsigned
             msgType = tr("Information");
             break;
         default:
-        msgType = title; // Use supplied title
+            break;
+        }
     }
+    // Append title to "Bitcoin - "
     if (!msgType.isEmpty())
         strTitle += " - " + msgType;
 
@@ -625,7 +632,7 @@ void BitcoinGUI::message(const QString &title, const QString &message, unsigned
         if (!(buttons = (QMessageBox::StandardButton)(style & CClientUIInterface::BTN_MASK)))
             buttons = QMessageBox::Ok;
 
-        QMessageBox mBox((QMessageBox::Icon)nMBoxIcon, strTitle, message, buttons);
+        QMessageBox mBox((QMessageBox::Icon)nMBoxIcon, strTitle, message, buttons, this);
         int r = mBox.exec();
         if (ret != NULL)
             *ret = r == QMessageBox::Ok;