Update application/models/grocery_crud_model.php

Changing num_rows to count_all, to optimize the SQL Select.
Update application/models/grocery_crud_model.php

Changing count_all to count_all_results, this way it can determine the number of rows in those Active Record queries. And adding the count feature to get_relation_total_rows
Merge pull request #150 from kjartano/master

Optimizing the SELECT statement for counting rows