* dgit sbuild: check that the set of .changes files found is as we
expect, before calling mergechanges.
* dgit sbuild: Rename the used-up .changes files to `.inmulti' to
- avoid accidental use of the wrong one (by software, or by users).
+ avoid accidental use of the wrong one (by software, or by users).
* dgit sbuild: Check that the binary .changes file doesn't contain a
.dsc.
* Introduce --rm-old-changes to delete previous builds' changes files.