shelve: move changegroup generation inside writebundle

We will generate different changegroup if general delta is enabled so we gather
this in the lower level function. There wasn't any good reason to have it in
the main code anyway.

hgext/shelve.py

@@ -105,7 +105,8 b' class shelvedfile(object):'
     def bundlerepo(self):
         return bundlerepo.bundlerepository(self.repo.baseui, self.repo.root,
                                            self.vfs.join(self.fname))
-    def writebundle(self, cg):
+    def writebundle(self, bases, node):
+        cg = changegroup.changegroupsubset(self.repo, bases, [node], 'shelve')
         changegroup.writebundle(self.ui, cg, self.fname, 'HG10BZ', self.vfs)
 
 class shelvedstate(object):
@@ -291,8 +292,7 b' def createcmd(ui, repo, pats, opts):'
             return 1
 
         bases = list(publicancestors(repo[node]))
-        cg = changegroup.changegroupsubset(repo, bases, [node], 'shelve')
-        shelvedfile(repo, name, 'hg').writebundle(cg)
+        shelvedfile(repo, name, 'hg').writebundle(bases, node)
         cmdutil.export(repo, [node],
                        fp=shelvedfile(repo, name, 'patch').opener('wb'),
                        opts=mdiff.diffopts(git=True))