table: add frequencies attribute to tableexprs
replace frequencies with count_values
Test for API compat
Use reader method for into(DataFrame, CSV)
Merge pull request #645 from cpcloud/csv-date-logic

Parse datetimes in CSV.reader
Use the correct variable in mongo testing
Merge pull request #660 from mrocklin/frequencies

Add frequencies attribute to tableexprs
Merge branch 'master' into sql-join-clean
py26 fix with dict comprehension