read_sql index_col does not accept tuple
#### Code Sample, a copy-pastable example if possible

```python
data = pandas.read_sql_query( sql, dbConn, index_col=('StartTime',equipCol) )

```
#### Problem description

The index_col argument does not accept a Python tuple, only a list. It should handle both.

#### Expected Output

#### Output of ``pd.show_versions()``

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.12.final.0
python-bits: 64
OS: Linux
OS-release: 4.4.0-59-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.17.1
nose: None
pip: 9.0.1
setuptools: 32.1.0
Cython: None
numpy: 1.11.0
scipy: 0.17.0
statsmodels: None
IPython: 5.1.0
sphinx: None
patsy: None
dateutil: 2.4.2
pytz: 2014.10
blosc: None
bottleneck: None
tables: None
numexpr: None
matplotlib: 1.5.1
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: 0.9999999
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
Jinja2: None
</details>
