Support Variable Binding with SQL Drivers

[theduckylittle]

Common practice for doing dynamic mapping is to pass in values from the URL. With read-only data sources this is fine but databases use SQL queries to source their data. When using the URL substitution methods with the databases this methodology can lead to potential SQL injection problems. In order to prevent these potential problems databases support variable binding. The database properly escapes the values and insulates itself from the injection attacks.

This ticket is a reflection of RFC 59.

[theduckylittle]

Initial version in r9876.