Bug behavior when checking element inclusion in non-unique MultiIndex 
I am using `pandas.__version__==0.14.0`.
This is my first bug report in github so excuse my possibly poorly formatted submission.

This bug report might be related to, or duplicate:
1. https://github.com/pydata/pandas/issues/2646
2. https://github.com/pydata/pandas/issues/6501

It was explained to me by [http://stackoverflow.com/users/1427416/brenbarn] on the following StackOverflow question, http://stackoverflow.com/questions/24683023/having-issue-with-hierarchical-index-set-behavior/24684844#24684844

Essentially,  the following behavior is not desirable:

```
print pd.__version__
WeirdIdx = pd.MultiIndex(levels=[[0], [1]],labels=[[0, 0], [0,0]],names=[u'X', u'Y'])
print WeirdIdx
print (0, 0) in WeirdIdx
print (1, 0) in WeirdIdx
print (100, 0) in WeirdIdx
print (100, 100) in WeirdIdx
```

since it prints:
    0.14.0
    X  Y
    0  1
       1
    True
    True
    True
    True

despite the fact that `(100,0)` and `(100,100)` are unambiguously not part of the index.
