[Perlfect-search] save space for inv_index_db

[Daniel Naber]

Hi Giorgos (everybody else may anser, too :-)

I noticed that inv_index_db stores the weight as a float, and these float 
values look like: 0.23232469323. If it would be enough to store only 0.23 
(in this case), then we could also multiply it by 100 and save as in short 
unsigned int (which is 0-65535).

This way we could make inv_index_db 30% smaller. Despite the fact that 
nobody cares about some hundred kilobytes anymore, does that make sense?

Regards
 Daniel