made the Reboot command first quit and then reboot

- fixed bug #989690
 - the installer now denies reboots while running
 - the Reboot instruction no longer returns or sets the error flag
 - added .onRebootFailed which is called when Reboot fails
 - installer should now always clean-up when rebooting


git-svn-id: https://svn.code.sf.net/p/nsis/code/NSIS/trunk@3729 212acab6-be3b-0410-9dea-997c60f758d6

Source/exehead/Ui.c

@@ -577,7 +577,12 @@ skipPage:
     m_curwnd = (HWND)wParam;
     goto skipPage;
   }
-  if (uMsg == WM_QUERYENDSESSION || (uMsg == WM_CLOSE && m_page == g_blocks[NB_PAGES].num - 1))
+  if (uMsg == WM_QUERYENDSESSION)
+  {
+    SetWindowLong(hwndDlg, DWL_MSGRESULT, FALSE);
+    return TRUE;
+  }
+  if (uMsg == WM_CLOSE && m_page == g_blocks[NB_PAGES].num - 1)
   {
     if (!IsWindowEnabled(m_hwndCancel))
     {