verify: extract "manifest" constant into variable

The "manifest" label that's used in error messages will instead be the
directory path for subdirectory manifests (not the root manifest), so
let's extract the constant to a variable already to make future
patches simpler.

mercurial/verify.py

@@ -205,20 +205,20 b' class verifier(object):'
         ui.status(_("checking manifests\n"))
         filenodes = {}
         seen = {}
+        label = "manifest"
         if self.refersmf:
             # Do not check manifest if there are only changelog entries with
             # null manifests.
-            self.checklog(mf, "manifest", 0)
+            self.checklog(mf, label, 0)
         total = len(mf)
         for i in mf:
             ui.progress(_('checking'), i, total=total, unit=_('manifests'))
             n = mf.node(i)
-            lr = self.checkentry(mf, i, n, seen, mflinkrevs.get(n, []),
-                                 "manifest")
+            lr = self.checkentry(mf, i, n, seen, mflinkrevs.get(n, []), label)
             if n in mflinkrevs:
                 del mflinkrevs[n]
             else:
-                self.err(lr, _("%s not in changesets") % short(n), "manifest")
+                self.err(lr, _("%s not in changesets") % short(n), label)
 
             try:
                 for f, fn in mf.readdelta(n).iteritems():
@@ -229,14 +229,14 b' class verifier(object):'
                             filenodes.setdefault(
                                 _normpath(f), {}).setdefault(fn, lr)
             except Exception as inst:
-                self.exc(lr, _("reading delta %s") % short(n), inst)
+                self.exc(lr, _("reading delta %s") % short(n), inst, label)
         ui.progress(_('checking'), None)
 
         if self.havemf:
             for c, m in sorted([(c, m) for m in mflinkrevs
                         for c in mflinkrevs[m]]):
                 self.err(c, _("changeset refers to unknown revision %s") %
-                         short(m), "manifest")
+                         short(m), label)
 
         return filenodes