use absolute imports in Visitor.py

Cython/Compiler/Visitor.py

@@ -4,15 +4,17 @@
 #   Tree visitor and transform framework
 #
 import inspect
-import TypeSlots
-import Builtin
-import Nodes
-import ExprNodes
-import Errors
-import DebugFlags
+
+from Cython.Compiler import TypeSlots
+from Cython.Compiler import Builtin
+from Cython.Compiler import Nodes
+from Cython.Compiler import ExprNodes
+from Cython.Compiler import Errors
+from Cython.Compiler import DebugFlags
 
 import cython
 
+
 class TreeVisitor(object):
     """
     Base class for writing visitors for a Cython tree, contains utilities for