convert timestamp values to datetime

Timestamp types were being ignored and treated as strings; this change
treats timestamps similarly as datetime types (ala pymysql and mysqldb).

Also included in this commit is a fix for the testConnectWithWrongDB
test which was asserting the error status code 1044 which is defined as
ER_DBACCESS_DENIED_ERROR instead of the expected ER_BAD_DB_ERROR 1049.
Merge pull request #31 from pdh/timestamp_datetime

convert timestamp values to datetime