Change c1 code processing.
c1 on tells screen to treat the input
characters between 128 and 159 as control functions. Such an 8-bit code
is normally the same as ESC followed by the corresponding 7-bit code. The
default setting is to process c1 codes and can be changed with the
defc1 command. Users with fonts that have usable
characters in the c1 positions may want to turn this off.