bundle: move writebundle() from changegroup.py to bundle2.py (API) writebundle() writes a bundle2 bundle or a plain changegroup1. Imagine away the "2" in "bundle2.py" for a moment and this change should makes sense. The bundle wraps the changegroup, so it makes sense that it knows about it. Another sign that this is correct is that the delayed import of bundle2 in changegroup goes away. I'll leave it for another time to remove the "2" in "bundle2.py" (alternatively, extract a new bundle.py from it).

--- a/mercurial/repair.py	Mon Mar 28 17:16:00 2016 -0500
+++ b/mercurial/repair.py	Mon Mar 28 14:41:29 2016 -0700
@@ -46,7 +46,7 @@
         bundletype = "HG10BZ"
     else:
         bundletype = "HG10UN"
-    return changegroup.writebundle(repo.ui, cg, name, bundletype, vfs,
+    return bundle2.writebundle(repo.ui, cg, name, bundletype, vfs,
                                    compression=comp)
 
 def _collectfiles(repo, striprev):