Code review comment for lp:~mandel/desktopcouch/fix_bug_519873

I suggested a solution to https://bugs.launchpad.net/desktopcouch/+bug/510232 on that bug's page, which I agree should probably be fixed first, which would make a nicer solution possible here. (Also not all lists would be mergeable lists, so any performance hit for very large lists would be circumventable by not making them mergeable lists.)