do_pwchange() is broken on SCO UnixWare 7

[Mike Thompson]

The do_pwchange() function in session.c needs to pass the username as an
argument to the passwd command. Without it, passwd always fails with
something like "passwd: unknown user" as if its getting a blank user
arg. It's strange but so are many other things in SCO, which BTW was NOT
my OS of choice :(

To make it work I simply changed line 1317 to this:
execl(_PATH_PASSWD_PROG, "passwd", s->pw->pw_name, (char*)NULL);