ENH: Update Cython imports.

scikits/image/graph/heap.pyx

@@ -35,7 +35,7 @@ from __future__ import division
 
 # cython specific imports
 import cython
-from stdlib cimport malloc, free
+from libc.stdlib cimport malloc, free
 
 cdef extern from "pyport.h":
   double Py_HUGE_VAL

scikits/image/opencv/opencv_backend.pyx

@@ -1,7 +1,7 @@
 import ctypes
 import numpy as np
 cimport numpy as np
-from python cimport *
+from cpython cimport *
 from opencv_constants import *
 from opencv_type cimport *
 from _libimport import cv, cxcore

scikits/image/opencv/opencv_cv.pyx

@@ -5,8 +5,8 @@ import ctypes
 cimport numpy as np
 import numpy as np
 
-from python cimport *
-from stdlib cimport *
+from cpython cimport *
+from libc.stdlib cimport *
 from opencv_type cimport *
 from opencv_backend import *
 from opencv_backend cimport *