Allow subclasses of groovy.sql.Sql to get ResultSet

In order for applications to perform optimally where multiple, large databases are in use, it can be important to iterate through a result set without using a closure. One use case is a merge of records from multiple databases: the company has several divisions and each has a an order database, each day, the orders for each SKU must be totalled across all divisions.

The desired solution is to submit a query to each of the databases in parallel.

String query = "select SKU, sum(Qty) from OrderItems group by SKU, order by SKU"

The results from the various DBs are then combined using a merge algorithm.

This cannot be accomplished with the current API, since it's impractical to load the results of the queries into List objects as is done by the rows(...) methods.

The attached patch provides a path to implementing the desired solution by adding new protected methods. It also refactors to consolidate logic and remove an exposure to NPE. In addition to new protect methods, a static method to create a List from a ResultSet is made public and the log field is made static.

The patch includes a new test case added to SqlTest.groovy