Series.isin(values) raises ValueError if values is a set
When trying to use `Series.isin(values)` for Timestamps, an exception is raised if `values` is a set.

```
d = {'Dates':[pd.Timestamp('2013-01-02'),
              pd.Timestamp('2013-01-03'),
              pd.Timestamp('2013-01-04')],
     'Num1':[1,2,3],
     'Num2':[-1,-2,-3]}

df = pd.DataFrame(data=d)

>>> df['Dates'].isin({pd.Timestamp('2013-01-04')})
ValueError: Buffer has wrong number of dimensions (expected 1, got 0)

>>> df['Dates'].isin([pd.Timestamp('2013-01-04')])
0    False
1    False
2     True
Name: Dates, dtype: bool
```
#### output of `pd.show_versions()`

```
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.11.final.0
python-bits: 64
OS: Linux
OS-release: 4.1.13-100.fc21.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_AU.utf8

pandas: 0.18.0
nose: None
pip: 8.1.1
setuptools: 20.2.2
Cython: None
numpy: 1.11.0
scipy: 0.17.0
statsmodels: None
xarray: 0.7.2
IPython: 4.1.2
sphinx: 1.3.5
patsy: None
dateutil: 2.4.2
pytz: 2015.7
blosc: None
bottleneck: 1.0.0
tables: 3.2.2
numexpr: 2.5.2
matplotlib: 1.5.1
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.8
boto: None
```
