Removed some possible name confusion in exercises.

doc/cifarSC2011/theano.txt

@@ -73,9 +73,9 @@ Exercise 1
 .. code-block:: python
 
   import theano
-  a = theano.tensor.vector("a") # declare variable
-  b = a + a**10                 # build symbolic expression
-  f = theano.function([a], b)   # compile function
+  a = theano.tensor.vector() # declare variable
+  out = a + a**10               # build symbolic expression
+  f = theano.function([a], out)   # compile function
   print f([0,1,2])
   # prints `array([0,2,1026])`