(tui_command_loop): New function to override gdb loop and make sure
uiout is set according to TUI mode.
(tui_command_loop): Install the specific TUI command hook.
* tuiIO.c (tui_initialize_io): Initialize tui_old_uiout.
(tui_uiout, tui_old_uiout): Make public.
* tuiIO.h (tui_uiout, tui_old_uiout): Declare.