Change score from float to int

For Drupal.org's index, the min and max scores are 0.01528500020504 and 13912. Our boosts are relatively low, 0.5, 2.0 and 3.0. Rounding down to powers of 10:

• Unsigned int max is 4,294,967,295, we can multiply by up to 100,000.
• Unsigned medium int max is 16,777,215, we can multiply by up to 1,000.

I suggest using 1,000 as a multiplier in an unsigned int, leaving plenty of room for higher boosts and addition as results are calculated. This will throw away some precision, but the scores in the DB engine aren't too precise anyway.

To get an idea of the effects, there is a score column on searches linked from #2136119: Text search on issue queues is slow and sometimes WSODs. I would be good with presenting the new ints instead of dividing again on output.

Attached is a patch for this.

The update is numbered sequentially after the update for #2170689: Use a (word, field_name) covering index on text tables. They can run in either order.

basic did some informal benchmarking, but we didn't save any numbers. It was roughly a 2x improvement.

When profiling queries for #2136119: Text search on issue queues is slow and sometimes WSODs, I saw that most of the time, by far is spent in either sorting or copying to tmp tables. This will help the sorts and sum(score). As far as I can tell, the benefits will be from processors being able to do multiple int operations per cycle in the core processor vs less per cycle in a separate unit. It will vary greatly depending on processor architecture, but I think good or a draw for all of them.