Avoid redundant queries + avoid redundant changes

Two changes here, which will help me a *lot* in avoiding redundant queries in a query-heavy request I have:

1. When saving translations, if some translations are already preloaded, save to *those* copies of the records rather than loading fresh copies from the database. This saves us both the initial fetch and the subsequent reloads.
2. If a field is set to its original value, it should not be marked as having changed, instead of "changing" from the original value to the original value.