DBAPI 2.0 broken when using dictionary as parameters

The function [pandas.io.sql._convert_params](https://github.com/pydata/pandas/blob/b77eb1f11bcd65515ac33e1510fe03fd365bc433/pandas/io/sql.py#L30-L35) assume that the parameters are passed as a list. However the [DBAPI2.0](http://legacy.python.org/dev/peps/pep-0249/#id14) specify that the parameters can be a list or a mapping. This is a regression compared to the current stable version 0.13.1.
