fixing the error in io/sql.py
Not able to find an testing module in for io/sql.py. And I don't have time to create one now. So I paste the testing code below, which can be added into pandas later on.

```
#!/usr/bin/env python

from pymysql import connect
from pandas.io.sql import read_frame

con = connect(host='genome-mysql.cse.ucsc.edu', user='genome', db='mm9')
sql = 'select geneName as symbol, name as refSeq, chrom, strand, txStart, txEnd from refFlat limit 5'
df = read_frame(sql, con)
print df
```
