ansi 11.6.2.2125
<CORE>
try to get a new input line from the SOURCE and set
>IN accordingly. Return a flag if sucessful, which is
always true if the current input comes from a
terminal and which is always false if the current input
comes from EVALUATE - and may be either if the
input comes from a file
reference: p4_refill in ../src/core.c:2359, export CO REFILL