I1401, I7094, ID16, ID32, ND100, PDP10, SAGE, VAX780, SCP: Declaration Hygiene

simh t_bool has been declared as int.  Given this, compilers didn't
notice inconsistent declarations with other int types.  These changes
fix those problems.

I1401: Consistently declare conv_old as t_bool

I7094: Consistently declare ch6_req_wr as returning t_stat

ID16, ID32: Consistently declare idc_wds as returning t_stat

ND100: Properly declare sim_load flag argument as int

PDP10: Consistently declare build_dib_tab as returning t_stat

SAGE: Properly declare sim_load flag argument as int

VAX780: Consistently declare rtfile_read as returning t_bool

TIMER: Properly declare sim_timer_cancel as returning t_stat

CONSOLE: Properly declare sim_os_fd_isatty as returning int

sim_timer.c

@@ -3515,7 +3515,7 @@ for (tmr=0; tmr<=SIM_NTIMERS; tmr++) {
 return FALSE;
 }
 
-t_bool sim_timer_cancel (UNIT *uptr)
+t_stat sim_timer_cancel (UNIT *uptr)
 {
 int32 tmr;