Replaced a number of $wpdb->escape() calls with esc_sql(). This fixes a bunch of "deprecated function" notices that showed up due to wpdb::escape() becoming deprecated in WP 3.6.

git-svn-id: https://plugins.svn.wordpress.org/broken-link-checker/trunk@751590 b8457f37-d9ea-0310-8a92-e5e31aec5664