new config system based on the execution of theano/config.py. Changed all call to os.getenv to use this file and put the config from gof/utils.py in the new file.

-pass verbose and version to new op generated by ConvOp.grad()

always register local_elemwise_fusion, but not in fast_run by default. Allow the test to work and test it event if not enabled.

added a fct to return the instance of the default mode. It check that it exist and raise an informative error if it don't exist.

changed comment to tell that we make a special case for scalar in all case into elemwise for the gpu.