Timestamp comparisons to Series should work on either side of the comparison operator
```
In [2]: df = DataFrame({'dates': date_range('20010101', periods=10)})

In [3]: Timestamp('20010109') < df.dates
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-3-713f2b228d0e> in <module>()
----> 1 Timestamp('20010109') < df.dates

/home/phillip/Documents/code/py/pandas/pandas/tslib.so in pandas.tslib._Timestamp.__richcmp__ (pandas/tslib.c:9555)()

TypeError: Cannot compare Timestamp with 'Series'
```

but when a `Series` is on the left hand side, things go swimmingly:

```
In [4]: df.dates < Timestamp('20010109')
Out[4]:
0     True
1     True
2     True
3     True
4     True
5     True
6     True
7     True
8    False
9    False
Name: dates, dtype: bool
```
