ftp/tnftpd: Update to 20231001

While I'm here:

• Switch to DISTVERSION as suggested by Porters Handbook
• Make use of NetBSD's CDN and add a few additional mirrors
• Add WWW url
• Add license:
  
  [1] tnftpd contains a mix of BSD2CLAUSE (mostly the NetBSD derived code) and BSD3CLAUSE (inherited from the orignal UCB BSD code).
  
  tnftpd was previously BSD4CLAUSE but that was fixed in the upstream code a while ago so I changed the COPYING to reflect that. It's no more restrictive than BSD3CLAUSE now.

ChangeLog:

• Release as "tnftpd 20231001".

• Always use $YACC even without --enable-maintainer-mode.

• Update to NetBSD-ftpd 20230930:
  • Fix uninitialized memory usage in count_users().
  • Fix pam_set_item() call with proper struct passed as

PAM_SOCKADDR.

• Build fixes:
  • Check for inet_net_pton() in -lresolv (for glibc).
  • Improve configure's display of make variables.
  • Remove deprecated autoconf macros.

• Security fixes:
  • CVE-2020-7468: Improve error handling when switching UID/GID.
  • Prevent MLSD and MLST before authentication succeeds.

• Update to NetBSD-ftpd 20230922:
  • Treat failed chdir/chroot for guest and chroot accounts as

fatal. Also treat failed set{e,}(u,g}id calls as fatal.
Addresses CVE-2020-7468, via FreeBSD.

• Improve seteuid error handling, per suggestion by Simon

Josefsson.

• Add missing check_login checks for MLST and MLSD.

• Sync libnetbsd replacements with NetBSD upstream:
  • Replace fgetln() with tools/compat implementation that

handles embedded NULs.

• Fix inet_net_pton() to avoid integer overflow in bits.
• Fix inet_ntop() to set errno when returning NULL.
• Fix inet_pton() to improve hex formatting.
• Fix sl_add() to not update size unless realloc() succeeds.

• Improve portability on NetBSD by providing own setprogname()

and getprogname(), instead of defining global __progname.

• Update example ftpusers to use example DNS and IP addresses.

• Build fixes:
  • Improve configure's display of detected features.
  • Enable more POSIX extensions.
  • Only replace glob() if required GLOB_ flags aren't available.
  • Only replace fts_open() if required FTS_ flags aren't

available.

Suggested by: [1] Luke Mewburn <lukem@NetBSD.org>
PR: 274209
MFH: 2023Q4

(cherry picked from commit 6845ef2aab7355c7f106d1cc207db69e5780ade4)