Add caching of load saved pickled files for datasets.
Fix circular import
Don't cache what isn't under PYLEARN2_DATA_PATH.
Remove timming as now Theano is ~20x faster in that case (for the second call).
Update url to point to the right place.
Allow the buildbot to pass extra parameters
Add missing import
pep8 remove from white list some of the file I changed.
Merge pull request #873 from nouiz/mixed

cache more stuff and disable others.
refactored show_negative_chains script
removed the patchviewer from the main function
added test for the show_negative_chains script
fixed stop number
refactored show_reconstruction script
fixed load_dataset function
reorganized imports
added tests for the show_reconstructions script and fixtures
refactored show_samples
added main test for dbm show_samples
fixed pep8