add capture_sql method to compare sql statements and compare

Other methods compare specific patterns, this method outputs
the actual sql query that is generated.
add test to compare sql statements in delete_all query

delete_all sql if an association is not loaded should behave
the same as if the association is loaded. This test ensures
the SQL statements are exactly the same.
fix delete_all to remove records directly

When delete_all is run on a CollectionProxy and has a
dependency of delete_all the SQL that is produced has an IN
statement. (DELETE FROM `associated_model` where `associated_model`
.`parent_id` = 1 AND `associated_model`.`id` IN (1, 2, 3...)).
This only happens if the association is not loaded (both loaded
and non-loaded delete_all should behave the same. This is a huge
problem when it comes to deleting many records because the query
becomes very slow. Instead the SQL produced should be (DELETE FROM
`assoicated_model` where `associated_model`.`parent_model_id`=1).

I fixed this by making sure the check for loaded and destroy also
makes sure that the dependent is not delete_all, so the conditional
goes to the else and deletes the records directly without the IN
statement.