BUG: fix 1xN mask on 1xN frame
TST: use DataFrame in the test
BUG: fix item cache invalidation bug in #3970 caused by is_mixed_type silently consolidating (hurf). also fix stable sorting bug presenting on my machine
Merge branch 'fix-consolidate-cache-invalidation-gh3970' of https://github.com/wesm/pandas into wesm-fix-consolidate-cache-invalidation-gh3970
CLN: have _consolidate_inplace invalidate the cache when needed
Merge pull request #4073 from cpcloud/internals-mask-edge-case

BUG: fix 1xN mask on 1xN frame
TST/BUG: fix 2to3 import rewrite of import pickle

In pandas.io.pickle the following statement will not allow python to import
anything due to the following rewrite by 2to3

import pickle -> from . import pickle

This make the import try to import itself ad infinitum and thus fails.
TST: make tox block when running in parallel