PyPy compatibility: esentially avoid pandas-related functionality and skipping some other test because NumPyPy does not pickle arrays yet.
Added default False to is_pypy.
Fixed the previous logic. It only checked for pandas-related stuff if pandas was installed, forgetting about the numpy possibilities.
Simplified logic using two main if flows, one for pandas objects and the other one for numpy objects.
Update to sync master.
Commented and unused pandas import.
Added skip decorators to downsample tests. Also capturing import error because the lack of SciPy.
Little refactoring adding some @Matheuz's suggestions.
Deleted unused commented code.
Used skipIfPyPy decorator in other places too.
Calling the is_py3 and is_pypy functions inside the custom decorators.
Passed custom decorator utils from server tests to the main test utils.
PEP8 compatibility.
Merge pull request #434 from damianavila/pypy-compat

PyPy compatibility: