ioctl_tty.2, poll.2, getpt.3, grantpt.3, openpty.3, posix_openpt.3, ptsname.3, ttynam...

ioctl_tty.2, poll.2, getpt.3, grantpt.3, openpty.3, posix_openpt.3, ptsname.3, ttyname.3, unlockpt.3, pts.4, pty.7: Eliminate problematic "master-slave" terminology

The "master-slave" terminology used in describing pseudoterminals
is problematic, and not even very technically descriptive. Rewrite
various manual pages to eliminate that language. The following
replacement terms are used:

slave ==> "terminal device"
       (or "terminal end of the pseudoterminal device pair")

master ==> "pseudoterminal device"
       (or "pseudoterminal end of the pseudoterminal device pair")

pseudoterminal (device) ==> "pseudoterminal device pair"

Another notable wording change is the use of phrasings such as
"the corresponding terminal device", when emphasizing the linkage
between the pseudoterminal and terminal ends of a pseudoterminal
device pair.

The terminology originates in golang (which made a similar
terminology change in 2019), and was suggested for Linux
man-pages by Elliot Hughes.

Reported-by: Elliott Hughes <enh@google.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>