I see your pull request, but I think it would work better to have a separate sqlfile extension vs trying to build it into Derby. I've generally found that databases that try to act like a different one tend to have incompatibilities still that are easier to manage in an extension that trying to push it into the real database's implementation.
I created https://github.com/liquibase/liquibase-sqlfire and will move your pull request logic into that repository.
Nathan