shell32: Keep at least one reference to the autocompletion object at initialization until the edit window is destroyed.

Spotted with Valgrind.

shell32: Store the autocompletion object pointer in a window property rather than in the window user data.

mshtml: Make sure previous request is stopped before starting new request in IPersistMoniker and IPersistStreamInit.

Changing the texture type has no effect at this point, and it wouldn't work
properly anyway.

msvcrt: Use the _set_error_mode value to switch between a dialogbox and stderr for C runtime messages.