Column downcase

When table columns in a Teradata database are defined as uppercase, the ActiveRecord code will initialize the Rails models based on those tables with uppercased attributes. This is similar to a problem addressed in other adapters such as [oracle_enhanced](https://github.com/rsim/oracle-enhanced).

The solution that I am including here is to downcase column names during the initialization of the TeradataColumn class, and also downcasing the returned attributes in the results returned by executing select statements.