verify: use appropriate local variable in "checkentry()"

Before this patch, "checkentry()" internal function uses both
"node"(argument of itself) and "n"(defined in outer of it) variables.

Because all callers of "checkentry()" use "n" to refer the object
which is passed to "checkentry()" as "node", both can refer same
object in "checkentry()". So, "checkentry()" works correctly.

But such usage is not good for independence of "checkentry()".

This patch replaces "n" in "checkentry()" with "node".

mercurial/verify.py

@@ -96,16 +96,16 b' def _verify(repo):'
             p1, p2 = obj.parents(node)
             if p1 not in seen and p1 != nullid:
                 err(lr, _("unknown parent 1 %s of %s") %
-                    (short(p1), short(n)), f)
+                    (short(p1), short(node)), f)
             if p2 not in seen and p2 != nullid:
                 err(lr, _("unknown parent 2 %s of %s") %
-                    (short(p2), short(n)), f)
+                    (short(p2), short(node)), f)
         except Exception, inst:
             exc(lr, _("checking parents of %s") % short(node), inst, f)
 
         if node in seen:
-            err(lr, _("duplicate revision %d (%d)") % (i, seen[n]), f)
-        seen[n] = i
+            err(lr, _("duplicate revision %d (%d)") % (i, seen[node]), f)
+        seen[node] = i
         return lr
 
     if os.path.exists(repo.sjoin("journal")):