Bring back the --dry-run options
Bring back the --resume-from option
Revert "BUGFIX: when committing a repository, prepare it on demand"

This reverts commit 7c250a508f23db2e507dc754c882f7f6f2b90dd7.
BUGFIX: Reference semantics bites!

The set of changed repositories was updated after commits were already
open; then we were closing repositories that had no current_ref.