update CClientUIInterface and remove orphan Wx stuff

- fix ThreadSafeMessageBox always displays error icon
- allow to specify MSG_ERROR / MSG_WARNING or MSG_INFORMATION without a
  custom caption / title
- allow to specify CClientUIInterface::ICON_ERROR / ICON_WARNING and
  ICON_INFORMATION (which is default) as message box icon
- remove CClientUIInterface::OK from ThreadSafeMessageBox-calls, as
  the OK button will be set as default, if none is specified
- prepend "Bitcoin - " to used captions
- rename BitcoinGUI::error() -> BitcoinGUI::message() and add function
  documentation
- change all style parameters and enum flags to unsigned
- update code to use that new API

- update Client- and WalletModel to use new BitcoinGUI::message() and
  rename the classes error() method into message()
- include the possibility to supply the wanted icon for messages from
  Client- and WalletModel via "style" parameter

src/noui.cpp

@@ -2,16 +2,33 @@
 // Copyright (c) 2009-2012 The Bitcoin developers
 // Distributed under the MIT/X11 software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
 #include "ui_interface.h"
 #include "init.h"
 #include "bitcoinrpc.h"
 
 #include <string>
 
-static int noui_ThreadSafeMessageBox(const std::string& message, const std::string& caption, int style)
+static int noui_ThreadSafeMessageBox(const std::string& message, const std::string& caption, unsigned int style)
 {
+    std::string strCaption;
+    // Check for usage of predefined caption
+    switch (style) {
+    case CClientUIInterface::MSG_ERROR:
+        strCaption += _("Error");
+        break;
+    case CClientUIInterface::MSG_WARNING:
+        strCaption += _("Warning");
+        break;
+    case CClientUIInterface::MSG_INFORMATION:
+        strCaption += _("Information");
+        break;
+    default:
+        strCaption += caption; // Use supplied caption
+    }
+
     printf("%s: %s\n", caption.c_str(), message.c_str());
-    fprintf(stderr, "%s: %s\n", caption.c_str(), message.c_str());
+    fprintf(stderr, "%s: %s\n", strCaption.c_str(), message.c_str());
     return 4;
 }