add mongo to travis script
travis: mongo - sudo apt-get mongodb-server
travis: oh, mongodb is on conda
travis: use travis mongodb
mongo: py3 compatibility
py26 compatibility
Merge branch 'mongo' into bcolz-chunks-mongo
chunks into list
copy blz tests to bcolz
expr: fix scalar invert/~ , add isnan to columnsyntax
expr: isnan and invert work more consistently
numpy: ~ compute
bcolz: selection defaults to blocking if numepxr fails