TST/CLN: legacy pickle testing
CLN:
- standardized testing data to live under tests/data (for that set of tests),
- added method `util/testing.get_data_path` to give you this path

TST:
- added `io/tests/test_pickle.py` and `io/tests/generate_legacy_pickles.py`
  to generate legacy pickle files and provide comparsions
  just run `python path_to_generate_legacy_pickles.py`
  
  it will create a version of pickle for that python version, arch, and system, and store in `pandas/io/tests/data/legacy_pickle/VERSION`
- sample pickles for windows-64/2.7/0.10.1 and linux/2.7/0.10.1 and linux/2.7/0.11.0 added
- need to run this on various combinations to generate the reference library
- allows backwards compatibility testing for these pickles
