Change references to cuaN in examples and documentation to ttySN.

Yes, rather linux-centric, I know.  Patch from Marco d'Itri
(Debian ppp package maintainer).

SETUP

@@ -21,7 +21,7 @@ administrator to create a file under /etc/ppp/peers, named for the ISP
 that you will be dialling.  For example, suppose the file is called
 /etc/ppp/peers/isp.  This file would contain something like this:
 
-cua0		# modem is connected to /dev/cua0
+ttyS0		# modem is connected to /dev/ttyS0
 38400		# run the serial port at 38400 baud
 crtscts		# use hardware flow control
 noauth		# don't require the ISP to authenticate itself

scripts/secure-card

@@ -17,14 +17,14 @@
 
 send_user "hello, starting ppp\n"
 
-system "stty 19200 -echoe -echo raw < /dev/cua3 > /dev/cua3"
+system "stty 19200 -echoe -echo raw < /dev/ttyS3 > /dev/ttyS3"
 
 #
 # These are the parameters for the program.
 #
 set user      Pxxxxxx
 set password  xxxxxxx 
-set modem     /dev/cua3
+set modem     /dev/ttyS3
 set dialup    <put phone number here>
 set timeout   60
 
@@ -107,5 +107,5 @@ expect {
 	}
 }
 
-overlay -0 $spawn_id -1 $spawn_id pppd /dev/cua3 19200 192.111.187.215: \
+overlay -0 $spawn_id -1 $spawn_id pppd /dev/ttyS3 19200 192.111.187.215: \
 	crtscts modem defaultroute debug