internal/v4: do not create new revision if content matches latest
internal/v4: minor changes for review
Merge pull request #115 from rogpeppe/051-detect-dupe

internal/v4: do not create new revision if content matches latest

When the content is the same as the latest version, there's no need to
bump the revision number. We needed to add another bundle to
test this, hence the change to the charm.v3 dependency.