Fix imports under Python 3.

skimage/viewer/canvastools/__init__.py

@@ -1,3 +1,3 @@
-from linetool import LineTool, ThickLineTool
-from recttool import RectangleTool
-from painttool import PaintTool
+from .linetool import LineTool, ThickLineTool
+from .recttool import RectangleTool
+from .painttool import PaintTool

skimage/viewer/canvastools/linetool.py

@@ -5,7 +5,7 @@ try:
 except ImportError:
     print("Could not import matplotlib -- skimage.viewer not available.")
 
-from base import CanvasToolBase, ToolHandles
+from .base import CanvasToolBase, ToolHandles
 
 
 __all__ = ['LineTool', 'ThickLineTool']

skimage/viewer/canvastools/painttool.py

@@ -8,7 +8,7 @@ try:
 except ImportError:
     print("Could not import matplotlib -- skimage.viewer not available.")
 
-from base import CanvasToolBase
+from .base import CanvasToolBase
 
 
 __all__ = ['PaintTool']

skimage/viewer/utils/__init__.py

@@ -1 +1 @@
-from core import *
+from .core import *

skimage/viewer/widgets/__init__.py

@@ -1,2 +1,2 @@
-from core import *
-from history import *
+from .core import *
+from .history import *