We just recently moved to a new internal configuration model for

controlling the rendering pipeline, but one call location (the FileDiff

API) was still using the old method. That'd be fine, except the old

method wasn't properly converting a request to disable syntax

highlighting.
This led to requests for diff data to return HTML versions of lines

instead of plain text.
The settings migration code now allows for disabling settings, and the

API has been updated for the new settings code.
Unit tests check to ensure that we're properly getting plain-text back

from it, unless requested otherwise.

Verified that the API returned plain text data for any diffs I queried.
A customer verified this fixed a regression they noticed.
Unit tests passed.