Apparent "bin" means don't set encoding

Rather than "binary".  Wonder if it's possible of needed to be able to change
the encoding of a PIO during its lifetime.  If it should be possible, I don't
think we can revert to "binary" at the moment.

src/core/PIO.pm

@@ -9,7 +9,7 @@ my role PIO {
     method !set-PIO-attributes(Mu :$PIO,:$chomp,:$bin,:$encoding,:$nl,:$enc) {
         $!chomp = $chomp // True;
         nqp::bindattr(self,$?CLASS,'$!PIO',nqp::decont($PIO)); # := doesn't work
-        self.encoding($bin ?? 'binary' !! $encoding // $enc // 'utf8');
+        self.encoding($encoding // $enc // 'utf8') unless $bin;
         self.nl($nl // "\n");
     }