Updated deprecated function WPDB::escape

WPDB::escape has been deprecated for security reasons. More information
here:
http://wordpress.org/support/topic/wordpress-36-rc2-last-minute-wpdbescape-deprecation-is-not-nice

404 Redirected was throwing the following:
Notice: wpdb::escape is deprecated since version 3.6! Use
wpdb::prepare() or esc_sql() instead. in
/var/www/html/wp-includes/functions.php on line 2919

Replaced all instances of 'wpdb->escape' with 'esc_sql' as suggested.
Since this is a pretty straight forward matter of replacing one escape
function with another, there shouldn't be any issues, but based on some
light testing, the plugin seems to be working properly and the notice is
gone.