Add a group_dot implementation for CPU.
And add the GPU version.
Fix import problem.
Fix names in the gpu implementation of GroupDotGrad.
Use the proper perform mechanism for GroupDotGrad.
Remove debugging code in the preform() for GpuGroupDot.
Fix c_code for GpuGroupDot so that it computes the same value.
Remove useless code from overrides of make_thunk
c_code for GpuGroupDotGrad
Small generalization fix for GroupDot c_code().
Stylistic changes to fit more into theano.
pep8/stylistic changes
Make the gpu opt for GroupDot check the node op and types of the inputs.
Since the grad of the grad is not implemented just don't define the function.
merged with arnauds