Handling of duplicate columns in pandas.io.sql.read_frame
Calling pandas.io.sql.read_frame can results in data frame with duplicate column names. For example when SQL query contains joins on tables with duplicate columns. 

Data frames with duplicate column names cause errors in many pandas functions. I can't even rename columns as df.columns = new_columns generates errors.

I think correct behavior would be for pandas.io.sql.read_frame have an option to "deduplicate" column names (for example by adding a number) or generate an error with duplicate column names.
