WL#873: Add Oracle like new_time() function for time conversion

This function allows to convert the time from one timezone to another, 
ie from "Helsinki" timezone to "Moscow" timezone.  
 
Usable ie in Web application, allowing user to specify in which timezone he 
would like to work with data.  
 
Open Source alternative implementation could be used for reference: 
http://www.weitz.de/timezone.html 
 
[later comment] 
 
This item partially duplicates worklog #345. But if we decide 
to cancel this item, we must update #345 to be broader. 
#345 talks only about conversion from localtime to arbitrary timezone, 
while #873 talks about conversion from any timezone to any timezone.