test: avoid using debugdrawdag in 'test-topic-debugcb.t'
The 'debugdrawdag' utility adds local tags that prevent hidden changeset to get
hidden. We will do without that extension for now.
# name space package to host third party extensionsfrom__future__importabsolute_importimportpkgutil__path__=pkgutil.extend_path(__path__,__name__)