putenv.3: Originated in SysVr2; in 4.3BSD-Reno; fixed on modern systems

putenv.3: Originated in SysVr2; in 4.3BSD-Reno; fixed on modern systems

Fixed in:
  NetBSD 6     src lib/libc/stdlib/putenv.c 1.13
  FreeBSD 7    putenv(3) says so
  OpenBSD 4.6  src lib/libc/stdlib/setenv.c 1.10
and is correct under current(?) MacOS as well

The current wording implies that all of 4.4BSD's descenants also carry
this bug (at least it did to me): they did until like 2009 but they're
fine now

Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Signed-off-by: Alejandro Colomar <alx@kernel.org>