FIX: Example code from tutorial page fails with conversion error

fix gh-1493 tutorial example that use undefined variable.

Fix exception/segfault newly introduced in gpujoin.

use absolute reference for abs_

For some reason this was failing before

http://deeplearning.net/software/theano/tutorial/examples.html fails with
conversion error, this change fix the problem.

SymPyCCode op

Change grad function name to "grad", not "prime"

Change y**2 test to y**3

Backport to python 2.4

Tests adv sub

add missing import

[WIP] Adding GpuJoin.c_code to cuda/basic_ops.py

doc: fix typo

Doc

Crash gpu reduce 1111