expr: merge on repeated columns raises error
dplyr: transform overwrites repeated columns
expr: fix merge overlapping columns error
expr: eval_str works on unicode literals
replace some instances of str with _strtypes or unicode
Merge pull request #512 from mrocklin/merge-repeated-columns

Merge repeated columns
Merge pull request #515 from mrocklin/str-lingering

Str lingering
Test relabel on Series objects
Implement relabel compute on Series and clean up a bit
Test map with rename
Allow renaming without a schema