fixed an issue where test_reshape in test_cuda_ndarray did not use the correct seed for random number generation

These tests were previously computing wrong values.

condition.

one that works on scalars.

previously introduced function for merging two slices.

Test that gemv are inserted into the graph. Disable the gemv test on complex as they don't get inserted.

re-use it for other optimizations.

optmized right now, and so they make no sense .. The code asks now for more
tests though.

interesting ones ?) with the disadvantage of making it slow

combinations of two subtensors.

include the length of the tensor as possible ``stop`` for a useless
subtensor.

changes done to the canonical form of the slice.

slices given the idx_list and the list of node inputs. The other function
transforms a slice into a canonical form ( where all entries are positives),
which makes dealing with slices much easier. I've also refractored the
perform of the Subtensor to use the first function ( since is mostly copy
paste from that code anyway)