agetty: 8 bit characters on the Linux console lead to input corruption

agetty: 8 bit characters on the Linux console lead to input corruption

8 bit characters on the Linux console lead to input corruption (e.g.
German umlauts). This is easily reproducable by inserting a login name with
umlaut and typing backspace afterwards.

agetty supports tty parity, which leads to getty treating these characters
as a 7bit char with set parity.

This patch by Samuel Thibault adds a new option -8 which disables parity
detection for ttys not used for serial logins.

| Note: With this patch, 8bit characters are just silently dropped (that's
| the expected getty behavior), this is quite neat since you then don't
| even need to backspace your 8bit characters :)

Signed-off-by: LaMont Jones <lamont@mmjgroup.com>