Don't assume process IDs fit in int.

Don't assume process IDs fit in int.

* emacs.c (shut_down_emacs) [!DOS_NT]:
* sysdep.c (sys_suspend) [SIGTSTP && !MSDOS]:
* term.c (dissociate_if_controlling_tty) [!DOS_NT]:
Use pid_t, not int, to store process IDs, as 'int'
is not wide enough on a few platforms (e.g., AIX and IRIX).