Consistent key name for conditional queries.

Following tags will either loc2 or loc3. 
```
<Sql id="loc2" limit="limit" when="empty $tz">
	select name, lat, lon, timezone as 'tz' from city where name like '$q%' and timezone = 'Asia/Kolkata'
</Sql>

<Sql id="loc3" limit="limit"  when="not empty $tz">
	select name, lat, lon, timezone as 'tz' from city where name like '$q%' and timezone = $tz
</Sql>
```