Add a method for counting the number of tuples a query returns.

Sparql in particular doesn't have a built-in counting construct; therefore,
a helper method is desirable to facilitate paging and the like.
Fix the test I broke.

... Too much Simpletest previously. :P
Fix the new test...

... Yep, definitely too much Simpletest.
Merge pull request #64 from adam-vessey/1.x-query-count-method

Add a method for counting the number of tuples a query returns.