logging out from "telnet" blows away all processes attached to your terminal

[Guy Harris]

Description:
	As its final act before "exit"ing, "telnetd" does a kill(0, SIGKILL).
	This is *extremely* antisocial, especially if you have done a "uucp"
	which starts up a "uucico".
Repeat-By:
	"telnet" to a 4.2BSD machine, start up a background job, and log out.
Fix:
	Get rid of the kill(0, SIGKILL) in "cleanup"; the "vhangup" there
	sends a SIGHUP, which is sufficient.

Thanks to Mark Plotnick, who discovered this problem both in "rlogind" and
"telnetd" and reminded me that "telnetd" had the same problem.