Change the default locale to C.UTF-8

The C.UTF-8 locales is the same as the actual C locale except it does support
the unicode character set. But the collation etc are still the same as the C
locale one.

Reviewed by:	many
Approved by:	many
Differential Revision:	https://reviews.freebsd.org/D26973

usr.bin/login/login.conf

@@ -47,8 +47,9 @@ default:\
 	:umtxp=unlimited:\
 	:priority=0:\
 	:ignoretime@:\
-	:umask=022:
-
+	:umask=022:\
+	:charset=UTF-8:\
+	:lang=C.UTF-8:
 
 #
 # A collection of common class names - forward them all to 'default'