Fixed node save hook

Both hook_gathercontent_pre_node_save_alter and hook_gathercontent_post_node_save are broken due to the invalid argument being passed. The $entity (NULL) should be replace with $node.

Replace
drupal_alter('gathercontent_pre_node_save', $entity, $content, $files);
module_invoke_all('gathercontent_post_node_save', $entity, $content, $files);

with
drupal_alter('gathercontent_pre_node_save', $node, $content, $files);
module_invoke_all('gathercontent_post_node_save', $node, $content, $files);