Merge branch 'master' into sender

lib/Slic3r/Print/Object.pm

@@ -308,7 +308,7 @@ sub slice {
     
     # remove empty layers from bottom
     while (@{$self->layers} && !@{$self->get_layer(0)->slices}) {
-        shift @{$self->layers};
+        $self->delete_layer(0);
         for (my $i = 0; $i <= $#{$self->layers}; $i++) {
             $self->get_layer($i)->set_id( $self->get_layer($i)->id-1 );
         }
@@ -319,7 +319,7 @@ sub slice {
         $self->_simplify_slices(scale($self->print->config->resolution));
     }
     
-    die "No layers were detected. You might want to repair your STL file(s) or check their size and retry.\n"
+    die "No layers were detected. You might want to repair your STL file(s) or check their size or thickness and retry.\n"
         if !@{$self->layers};
     
     $self->set_typed_slices(0);