Format PDO statement with bind/values replacement

This replaces PDO binds such as 'key_name = :name' with corresponding array values, eg array('name'=>'some value')
This is merely a cosmetic replacement to allow for readability: the result WILL NOT be valid SQL! (eg no proper quotes)

@since  1.7.3
@param  string $statement  SQL query with PDO style named placeholders
@param  array  $values     Optional array of values corresponding to placeholders
@return string             Readable SQL query with placeholders replaced