2. update datasets.

2. fix two dimension bugs in model selection function when computing std.

2. correct an error in the common walk kernel. DON NOT use the old one.
3. improve the method to construct fully-labeled direct product graphs, much faster for sparse graphs.

2. model_selection_precomputed can now save all results as human readable text.
3. modify pygraph.utils.utils.floydTransformation and pygraph.utils.graphdataset.get_dataset_attributes.