Fix a one-character typo. The effects of which were "Console"->"Ttys" menu
would not launch (and gave no error). This was easily diagnosed by running
`bsdconfig -d' as root and seeing the following error right after selecting
the "Ttys" sub-menu:

DEBUG: f_getvar: var=[text] value=[
Error: Expected at least 6 tokens for --menu, have 4.
Use --help to list options.] r=0

Typo was introduced by SVN r251361.
Prevent getting hung-up on the following prompt (found while testing with
`chflags schg /etc/ttys'):

override rw-r--r--  root/wheel for /etc/ttys? (y/n [n])

Simply by adding `-f' flag to mv(1).
Don't silently ignore errors (found while
testing with `chflags schg /etc/ttys).
Fix a typo in comments.