bundle: condition the changegroup part when creating a new bundle

We will generate stream bundle in the next changesets which doesn't need the
changegroup part.

Differential Revision: https://phab.mercurial-scm.org/D1951

mercurial/bundle2.py

@@ -1577,7 +1577,9 b' def _addpartsfromopts(ui, repo, bundler,'
     # different right now. So we keep them separated for now for the sake of
     # simplicity.
 
-    # we always want a changegroup in such bundle
+    # we might not always want a changegroup in such bundle, for example in
+    # stream bundles
+    if opts.get('changegroup', True):
     cgversion = opts.get('cg.version')
     if cgversion is None:
         cgversion = changegroup.safeversion(repo)

mercurial/commands.py

@@ -1263,7 +1263,7 b' def bundle(ui, repo, fname, dest=None, *'
         compopts['level'] = complevel
 
 
-    contentopts = {'cg.version': cgversion}
+    contentopts = {'cg.version': cgversion, 'changegroup': True}
     if repo.ui.configbool('experimental', 'evolution.bundle-obsmarker'):
         contentopts['obsolescence'] = True
     if repo.ui.configbool('experimental', 'bundle-phases'):