add into(DataFrame, pytables Table)
fix h5py/pytables import interactions
convert test to use pytest fixtures
use importorskip in fixture as idiom for skipping single test
Merge branch 'master' of github.com:ContinuumIO/blaze into into_pytables_df

Conflicts:
	blaze/api/tests/test_into.py
use consistent technique to skip tests based on import behavior
comprehensive compute tests
mongo: distinct
add pymongo to comprehensive compute test
a few additions to compute test_comprehensive
Merge pull request #455 from talumbau/into_pytables_df

add into(DataFrame, pytables Table)
Merge branch 'master' into compute-comprehensive
DataFrame -> pd.DataFrame in into.py
compute: only add mongo source if pymongo exists
try-except mongo imports
compute: avoid bcolz testing issue

This bcolz issue https://github.com/Blosc/bcolz/issues/37 was
intermittently causing errors in tests after selections were used.

We can avoid this issue by having pretty lame selection tests.
expr: Summary
expr: summary hashable and eval(str(.)) able
python: Summary compute
scalar: name, dtype properties
expr: Reductions support Number interface