buglets with pts - with patch

I found a couple of display issues with the new pts type ptys.

wall and who - don't check the utmp tty validity (see also PR bin/84041)
	The attached patch duplicates the check from the w program in who and
wall. For some reason closed pts ttys are displayed/printed to when
there wasn't a problem with the old pty implementation.

ps - the TT column displays garbage (always "pts")
	The attached patch trims "pts/" from the tty name. The printout doesn't
look nice ("10443 pts  IWs    0:00,00 bash" changes to "10443   3  IWs
0:00,00 bash") but the field width is 4 which doesn't allow much. The
right solution would probably involve removing TT column and always use
the longer version TTY with width of 8 (which allows to correctly
display "pts/3"). I checked Solaris 10 and it displays the full tty name
by default.

Regards

Michal