Don't install keyboard hook when debugged on MS-Windows

Don't install keyboard hook when debugged on MS-Windows

* src/w32fns.c (setup_w32_kbdhook): Don't install the keyboard
hook if we are being debugged.  This avoids hosing the debugger,
because the hook is global, and is called in the context of the
thread which installed it, and that thread is stopped when GDB has
control.  Reported by Fabrice Popineau <fabrice.popineau@gmail.com>.