Allow for WP bug #23268

Ref: http://codex.wordpress.org/Class_Reference/WP_Query#Custom_Field_Parameters
Ref: http://core.trac.wordpress.org/ticket/23268

Found these while doing a quick search round for any other queries on meta values which may or may not account for the defaults no longer being saved (inspired by issue #838). All those queries seemed to be fine at first glance.
Searched on `meta_query`, `meta_key` and `meta_value`.