shelve: look for shelved node in the repository before unbundling

This prepares the version of shelve that would not strip the shelved node from
the repository. If we have the node information, search for it in the
repository and only fallback on unbundling if it is missing.

To be able to find such nodes, we operate on an unfiltered repository.

hgext/shelve.py

@@ -764,9 +764,15 b' def _commitworkingcopychanges(ui, repo, '
 def _unshelverestorecommit(ui, repo, basename):
     """Recreate commit in the repository during the unshelve"""
     repo = repo.unfiltered()
+    if shelvedfile(repo, basename, 'shelve').exists():
+        node = shelvedfile(repo, basename, 'shelve').readinfo()['node']
+    if node is None or node not in repo:
     with ui.configoverride({('ui', 'quiet'): True}):
         shelvedfile(repo, basename, 'hg').applybundle()
         shelvectx = repo['tip']
+    else:
+        shelvectx = repo[node]
+
     return repo, shelvectx
 
 def _rebaserestoredcommit(ui, repo, opts, tr, oldtiprev, basename, pctx,