Fix the naming of the fallback import from the previous change.
Fix the naming of the fallback import from the previous change.

The fallback import, `SortedDict`, was not being renamed to
`OrderedDict`, meaning that code was still broken when on older versions
of Python. This fixes up the name to be aliased properly.

reviewboard/reviewboard,chipx86/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,chipx86/reviewboard,reviewboard/reviewboard