Get rid of most calls to $Slic3r::flow

lib/Slic3r/Polygon.pm

@@ -118,7 +118,7 @@ sub subdivide {
 # returns false if the polyline is too tight to be printed
 sub is_printable {
     my $self = shift;
-    my ($flow_width) = @_;
+    my ($flow) = @_;
     
     # try to get an inwards offset
     # for a distance equal to half of the extrusion width;
@@ -129,7 +129,7 @@ sub is_printable {
     # detect them and we would be discarding them.
     my $p = $self->clone;
     $p->make_counter_clockwise;
-    return $p->offset(Slic3r::Geometry::scale($flow_width || $Slic3r::flow->width) / 2) ? 1 : 0;
+    return $p->offset($flow->scaled_width / 2) ? 1 : 0;
 }
 
 sub is_valid {