Reuse theano.compat.cmp. (Suggested by @lamblin.)

theano/gof/tests/test_link.py

@@ -5,14 +5,9 @@ from theano.gof.graph import Variable, Apply, Constant
 from theano.gof.type import Type
 from theano.gof.op import Op
 from theano.gof import fg
-from theano.gof import toolbox
 
 from theano.gof.link import *
-try:
-    cmp
-except NameError:
-    def cmp(a, b):
-        return (a > b) - (a < b)
+from theano.compat import cmp
 
 def as_variable(x):
     assert isinstance(x, Variable)