exchange: add "streaming all changes" to bundle2 pulling

This is the beginning of client-side support for performing a stream
clone using bundle2. The main bundle2 pull function checks whether to
perform a streaming clone and outputs a message if so.

While we have a duplicate message, it seems easier to have all the
bundle2 console writing in one location and in an easy-to-read
conditional block.

mercurial/exchange.py

@@ -1075,6 +1075,9 b' def _pullbundle2(pullop):'
 
     For now, the only supported data are changegroup."""
     kwargs = {'bundlecaps': caps20to10(pullop.repo)}
+
+    streaming, streamreqs = streamclone.canperformstreamclone(pullop)
+
     # pulling changegroup
     pullop.stepsdone.add('changegroup')
 
@@ -1087,7 +1090,9 b' def _pullbundle2(pullop):'
             # make sure to always includes bookmark data when migrating
             # `hg incoming --bundle` to using this function.
             kwargs['listkeys'].append('bookmarks')
-    if not pullop.fetch:
+    if streaming:
+        pullop.repo.ui.status(_('streaming all changes\n'))
+    elif not pullop.fetch:
         pullop.repo.ui.status(_("no changes found\n"))
         pullop.cgresult = 0
     else: