scipy.signal.convolve2d causes errors on atexit. i moved imports to make it possible to use our convolve op without triggering this problem

self). Also did some housecleaning

* typo in c_code (comparing type instead of type.dtype)
* added test case for 3D input tensor in test_ConvOpGrad

Raise a NotImplementedError.

This is because the gradient on the weights is obtained by convoling the visible
layer with the hidden layer (as the kernel). Problem is the convolution code
does not support kernels larger than the input image (which is the case in full
mode). Either fix ConvOp to allow this, or maybe convolve the hidden with the
visible as the kernel, then DimShuffle at the end.

multiple input features

debugmode now checks strides all the time, with the option of raising an exception instead of logging to stderr