add parameterised value support for text

This allows support for text types to be parameters however TDS dose not allow text to be ouput parameters so that is not supported as well as I had some issue with empty string such as '' from my understanding it my not be supported (http://lists.ibiblio.org/pipermail/freetds/2010q2/025787.html) and if so the test case for it should either be removed or modified.

Signed-off-by: Zach Aller <zachaller@hotmail.com>