The ornamental design for a slacksetter, as shown and described.
FIG. 1 is a top plan view of an ornamental design for a slack setter of the present invention in a first configuration;
FIG. 2 is a front view of an ornamental design for a slack setter of the present invention in a first configuration;
FIG. 3 is a right side view of an ornamental design for a slack setter of the present invention in a first configuration;
FIG. 4 is a rear view of an ornamental design for a slack setter of the present invention in a first configuration;
FIG. 5 is a left side view of an ornamental design for a slack setter of the present invention in a first configuration;
FIG. 6 is a bottom plan view of an ornamental design for a slack setter of the present invention in a first configuration;
FIG. 7 is a front end isometric view of an ornamental design for a slack setter of the present invention in a first configuration; and,
FIG. 8 is a rear end isometric view of an ornamental design for a slack setter of the present invention in a first configuration.
The broken line showing of structural features is included for the purpose of illustrating non-claimed subject matter and forms no part of the claimed design.