Add better tests for new prepared_statements

[jwilberding]

Right now it is hard to test the new method of specifying prepared_statements, as it requires we bootstrap a separate app that has the sqerl_rec behavior. Right now the current test basically tests that including {app, sqerl} doesn't break anything, but it isn't really testing to see if the module introspection is working, since the test modules with the sqerl_rec behavior do not have an associated app we test with.

Relevant code:
https://github.com/opscode/sqerl/blob/master/test/sqerl_rec_tests.erl#L143
https://github.com/opscode/sqerl/blob/master/test/sqerl_test_helper.erl#L19-L20