We provide a compatibility patch that fixes certain versions of SQLite

with Django prior to 2.1.5.
This patch made the assumption that it could import the Django SQLite

backend at the module level, since SQLite is built into Python. However,

on modern versions of Django, this will fail to import if the version of

SQLite is too old.
We now import this only if we're about to apply the patch, in which case

we've already confirmed the compatible version range.

Tested on reviews.reviewboard.org, where this problem was first encountered

due to an older SQLite. We no longer hit a premature import.