Alternatively, I could just ignore the problem. `Counter` is only needed to format the output of an Error message. Given that most people use at least python 2.7, I could live with a slightly different error message for those few people who are still on 2.6. (Instead of `'IPAC DBMS tables are not case sensitive. This causes dublicate column names: {0}'.format(doublenames)` users in 2.6 would see `'IPAC DBMS tables are not case sensitive. This causes dublicate column names.'`.)

The actual test in https://github.com/astropy/astropy/pull/1152/files#L0R380 if a column name is non-unique after converting all column names to lower case can be done as `if len(namelist) != len(set(namelist))` which works in 2.6 as well.
Defining the Counter object just to list the duplicated column names for IPAC/DBMS tables, if they exist in tables of python 2.6 user seems like a lot of code for a situation that probably never ever comes up.