BUG/API: df['col'] = value and df.loc[:,'col'] = value are now completely equivalent
previously the .loc would not necessarily coerce the dtype of the resultant series
closes #6149

this refues to pass py2.6 and I cannot duplicate this error with the exact same virtual env....if
i can't fix it by tomorrow...will move to 0.14
 this exposed an odd bug, which is fairly tricky to fix...so moving to 0.14
