Mixed stuff: pep8, comments, doc, don't enable GpuConv*3D op by default at that module import.

I don't want to place more detail since I don't want this to be a full discourse on the finer details of theano optimization.

Basically, no graph replacement will ever be performed around this, if the infer_shape is not provided, then no shape info will be gathered, and it will probably not support any future node information we may add.

But if that is not a concern for you, then ok, remove it.  Just don't add the sentence you've added.