Suggest that we add hook to allow other modules to modify visibility

Modules like block_query need to have their visibility respected as well - I suggest we add a hook to context respect to allow other modules to implement their context respect.

-            if ($page_match && $role_match) {
+            $visibility = module_invoke_all('context_respect_block', $block);
+            if ($page_match && $role_match && !in_array(true,$visibility)) {