qtui.h/noui.h interface cleanup

- rename wxMessageBox, remove redundant arguments to noui/qtui calls
- also, add flag to force blocking, modal dialog box for disk space warning etc
- clarify function naming
- no more special MessageBox needed from AppInit2, as window object is created before calling AppInit2

src/util.cpp

@@ -1041,7 +1041,7 @@ void AddTimeData(const CNetAddr& ip, int64 nTime)
                     string strMessage = _("Warning: Please check that your computer's date and time are correct.  If your clock is wrong Bitcoin will not work properly.");
                     strMiscWarning = strMessage;
                     printf("*** %s\n", strMessage.c_str());
-                    boost::thread(boost::bind(ThreadSafeMessageBox, strMessage+" ", string("Bitcoin"), wxOK | wxICON_EXCLAMATION, (wxWindow*)NULL, -1, -1));
+                    ThreadSafeMessageBox(strMessage+" ", string("Bitcoin"), wxOK | wxICON_EXCLAMATION);
                 }
             }
         }