Timestamp equality broadcasts incorrectly
Always returns true for equality and inequality:

``` python
In [168]: t = pd.Timestamp('2000-01-29 01:59:00')

In [169]: a = pd.Series([t])

In [170]: b = pd.Series([t])

In [171]: a
Out[171]:
0   2000-01-29 01:59:00
dtype: datetime64[ns]

In [172]: a == b
Out[172]:
0    True
dtype: bool

In [173]: a != b
Out[173]:
0    True
dtype: bool

In [174]: t == t
Out[174]: True

In [175]: t != t
Out[175]: False
```
