make rename*rename scale better
make rename*rename scale better

test case 1436:
  f0, f1 exist and point to different inodes
  rename("f0", "f0") -> ok
  rename("f1", "f0") -> ok
apply the "Don't read unless necessary" pattern

bowlofstew/sv6,aclements/sv6,aclements/sv6,aclements/sv6,bowlofstew/sv6,bowlofstew/sv6,bowlofstew/sv6,aclements/sv6,aclements/sv6,bowlofstew/sv6