to separate the open(/dev/ptm) from the ioctl(PTMGET) for privilege
separation or pledge().
Based on a diff from reyk@.
ok deraadt millert

through all existing pseudo-tty devices in /dev.

fixes pr #3998; diff from frank denis, though slightly different fix
committed;
help and ok millert@

ioctl(2), an unprivileged process may allocate a pty and have its owner
and mode set appropriately.  This means that programs such as xterm and
screen no longer need to be setuid.  Programs using the openpty()
function require zero changes and will "just work".
Designed by beck@ and deraadt@; changes by beck@ with cleanup (and
a rewrite of the vnode bits) by art@ and tweaks/bugfixes by me.
Tested by many.

rescinded 22 July 1999.  Proofed by myself and Theo.

- clean up .Xr's

- new sentence, new line

o) always close .Bl tags;
o) fix usage of .Xr;
millert@ ok

it's not supposed to be a hyphen/dash

- correct two .Fn references to forkpty()
- describe retval of forkpty(); it can return PID as well
- add xref to fork(2)