Merge branch 'ds/bundle-uri-5'

The bundle-URI subsystem adds support for creation-token heuristics to help incremental fetches. * ds/bundle-uri-5: bundle-uri: test missing bundles with heuristic bundle-uri: store fetch.bundleCreationToken fetch: fetch from an external bundle URI bundle-uri: drop bundle.flag from design doc clone: set fetch.bundleURI if appropriate bundle-uri: download in creationToken order bundle-uri: parse bundle.<id>.creationToken values bundle-uri: parse bundle.heuristic=creationToken t5558: add tests for creationToken heuristic bundle: verify using check_connected() bundle: test unbundling with incomplete history