expr: boolean fixes

Scalar boolean interface

isnan attribute on tables

Not uses operator.invert, not operator.not
add chunks
add bcolz
numpy: union, not, chunks
into: pass kwargs in type and DataFrame <- tuple
python: distinct works on lists
into: numpy <- list, datetime handling
add bcolz and chunks to __init__
bcolz: use streaming python by default

At least for Selections, By, distinct, rowwise, and nunique

Using NumPy chunks for reductions
add bcolz to testing scripts
bcolz: skip tests if no bcolz
Merge pull request #456 from mrocklin/boolean-fixes

expr: boolean fixes
into: error message
into: list <- dict_items (python 3)
Merge pull request #457 from mrocklin/bcolz2

Add BColz and chunking backend
into: exhaustive n by m test
into: np.ndarray maintains type information
into: nd.array <- Table passes dtype/datashape information
into: bcolz.ctable <- Table(list, ...)
into: np.ndarray <- DataFrame using to_records