repair: extract a helper for generating all manifest revlogs

We'll need to walk the manifest revlogs also to figure out which
manifests have linkrevs out of order (for fixing the bug shown in the
previous patch).

By the way, perhaps it would be more efficient in many cases to find
only the relevant directory manifest revlogs based on the files
instead of walking the entire store, but that can be changed later.

Differential Revision: https://phab.mercurial-scm.org/D6794

mercurial/repair.py

@@ -364,11 +364,11 b' def delayedstrip(ui, repo, nodelist, top'
     callback.addnodes(nodelist)
 
 def stripmanifest(repo, striprev, tr, files):
-    revlog = repo.manifestlog.getstorage(b'')
-    revlog.strip(striprev, tr)
-    striptrees(repo, tr, striprev, files)
+    for revlog in manifestrevlogs(repo):
+        revlog.strip(striprev, tr)
 
-def striptrees(repo, tr, striprev, files):
+def manifestrevlogs(repo):
+    yield repo.manifestlog.getstorage(b'')
     if 'treemanifest' in repo.requirements:
         # This logic is safe if treemanifest isn't enabled, but also
         # pointless, so we skip it if treemanifest isn't enabled.
@@ -376,7 +376,7 b' def striptrees(repo, tr, striprev, files'
             if (unencoded.startswith('meta/') and
                 unencoded.endswith('00manifest.i')):
                 dir = unencoded[5:-12]
-                repo.manifestlog.getstorage(dir).strip(striprev, tr)
+                yield repo.manifestlog.getstorage(dir)
 
 def rebuildfncache(ui, repo):
     """Rebuilds the fncache file from repo history.