Fix plaintext URLs not being detected if they're the very first thing in a post (with no preceding whitespace, etc).

git-svn-id: https://plugins.svn.wordpress.org/broken-link-checker/trunk@957918 b8457f37-d9ea-0310-8a92-e5e31aec5664
Replace the deprecated like_esc() function with $wpdb->esc_like() where available.

git-svn-id: https://plugins.svn.wordpress.org/broken-link-checker/trunk@957919 b8457f37-d9ea-0310-8a92-e5e31aec5664