There are a few places where we are querying for DiffCommits but aren't

providing an ORDER BY clause, so we get them in whatever order the

database provides. SQLite returns them by primary key, but MySQL does

not, which leads to commits being out of order is certain places (such

as the CommitListField in change descriptions).
We always want DiffCommits ordered by primary key, so we make that the

default. Any query in which this is not the case can explicitly provide

an ORDER BY clause.

Ran unit tests.