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