Checking if module og_access exist to view permission, also working on new simple test for the new functions 

Modified a case of node view access, when the node content is set to default access, treat as private if permmision was alreaty set in the grant array. 

Added hook_node_access_records_alter() to allow view permission to a user subgroups, even if he's not member of the sub group.
Also I extended og_subgroups_get_reverse_hierarchy_tree_perm() function to return the reverse tree structure with level information.