The Summary column in 2.5 switched to using format_html(), but was using

it in a way that was incompatible with Python 2.6. This wasn't caught

due to the lack of unit tests.
We now use specific positional arguments ({0}, {1}) instead of generic

arguments ({}), in order to retain compatibility.
Unit tests were added for all variations on the column's rendered

output.

Unit tests pass on Python 2.6 and 2.7.