If a diff file with a comma in the filename was uploaded via the web UI, clicking "Download Diff" could present an error about "Multiple Content-Disposition" when running with Chrome 16 or newer.
The problem is that we use the Content-Disposition header to tell the browser what filename to save as, but commas in this header are interpreted as multiple values.
To fix this, before we assemble the Content-Disposition header, we replace all commas in the diffset filename with underscores.

Wrote a unit test, in the test, I set the diffset.name as 'test, comma'.
Unit test passed.
Unit test failed whitout the fix.