SQL: test with oldest supported sqlalchemy
Noticed when looking at #9083 that we used an sqlalchemy feature in #8926 that is not supported in at least sqlalchemy 

Concrete, it is about `import sqlalchemy.sql.type_api as type_api` (https://github.com/pydata/pandas/blob/v0.15.2/pandas/io/sql.py#L1162). I cannot import this 0.8.2 (and in any case, this should better be `sqlalchemy.types.TypeEngine` instead of `type_api.TypeEngine`)

We should check if we test older slqalchemy versions (0.8.x series, or even 0.7.x series?), or why this has not been caught by the tests.
