* main.c (main): Remove calls to {pre,post}_add_symbol_hooks.

    * main.c (main): Remove calls to {pre,post}_add_symbol_hooks.
        There should be sufficient information/hooks now to eliminate
        this hack.

        * exec.c (file_command): Add a new hook here to inform ui's
        when the exec file has changed. Adding it here allows the
        ui to be informed after symbol reading.

        * gdbcore.h: Add declaration of file_changed_hook.