Fix stack use after scope in libutil/pty

The pt variable's elements are used after the end of the pt scope.
A move of pt to outer scope fixes this.

Detected with MKSANITIZER/ASan with tmux(1), a forkpty(3) user.

branches: 1.31.38; 1.31.44;
remove pointless static.

branches: 1.30.2;
fix -Wsign-compare issues

Use the re-entrant getgr*_r functions. From John Nemeth.

If TIOCPTMGET fails, close /dev/ptm.

Don't give write privileges at all if the tty group is missing.

I really want to kill the hard-coding of _TTY_GID. Set the group to the
primary group of the user if the group tty does not exist.

KNF; Simplify some logic, so that lines don't wrap. Explain why we
break, continue, or return from the tty scanning loops.

openpty: just check errors of syscalls,
instead of checking permission beforehand in userland.

Don't allow openpty to succeed if the caller is non-superuser.
XXX: we cross-reference ptm 4 which does not exist (yet)

use the pty multiplexor if it exists.

remove unused variable

Move UCB-licensed code from 4-clause to 3-clause licence.

Patches provided by Joel Baker in PR 22280, verified by myself.

Fix openpty() so that it correctly scans the entire list of possible
ttys. The new ttys (g-zA-Z) are "optional", since they may not be
present, and their absence is not a "fatal" error.

Add support for up to 930 pty devices (instead of the current 256).

The openpty() routine has been modified to use the extra pty names
before the "traditional" names, so that programs too dumb to use
openpty() will, hopefully, find one of the "traditional" ptys free
even if many others are in use. The modifications to MAKEDEV are
courtesy Andrew Brown, and are pretty clever: the unit numbers used
by the "traditional" names stay the same, to avoid trouble when
upgrading existing systems. The unusual use of "dd" to index an
array in MAKEDEV is because no other simple method seemed feasible
using only the programs on the install media for all ports.

revert over-zealous pcvt cull; we still need to skip ttyv* whilst pccons uses
ttyv0 on some ports (currently; arm32, bebox, i386, prep). should fix PR 12862.

Remove PCVT hack.

- __RCSID() police.
- ANSIfy.
- Miscellaneous style changes.
- Shutup lint(1) in one or two cases.

branches: 1.14.8;
back out the #ifdef _DIAGNOSTIC argument checks; too many people complained.
_DIAGASSERT() is still retained.

* use _DIAGASSERT() to check pointer arguments against NULL and file
descriptors against -1 (as appropriate).
* add actual checks which to detect stuff that would trigger_DIAGASSERT(),
and attempt to return a sane error condition.
* knf some code
* remove some `register' decls.

the first two items result in the addition of code similar to the
following in various functions:

_DIAGASSERT(path != NULL)
#ifdef _DIAGNOSTIC
if (path == NULL) {
errno = EFAULT;
return (-1);
}
#endif

More trailing white space.

Delint

unregisterify

merge with lite-2

- RCSID police
- Add ttymsg.3

Make openpty() work more than once.

branches: 1.6.4;
Minor reorganization of libutil, including the addition of passward
locking and editing functions.
From Greg Hudson <ghudson@MIT.EDU>

Prototypes (PR#1100).

minor cleanup; kill unnecessary casts

Support up to 256 ptys.

Add RCS identifiers.

branches: 1.1.1;
Initial revision