Bundle URIs part 4.
* ds/bundle-uri-4:
clone: unbundle the advertised bundles
bundle-uri: download bundles from an advertised list
bundle-uri: allow relative URLs in bundle lists
strbuf: introduce strbuf_strip_file_from_path()
bundle-uri: serve bundle.* keys from config
bundle-uri client: add helper for testing server
transport: rename got_remote_heads
bundle-uri client: add boolean transfer.bundleURI setting
clone: request the 'bundle-uri' command when available
t: create test harness for 'bundle-uri' command
protocol v2: add server-side "bundle-uri" skeleton