[PATCH] Speedup associations preloading when multiple options are used in :include (2.3.x branch)

Hello,

When ActiveRecord's find() option :include => [a lot of stuff], the current association preloading code may be not very efficient, because it calls flatten.compact.uniq for each option for :include.

This can be done only once, and this really improves performance when there are hundreds of records for which associations are preloaded.

The fix is very simple, please see the attached patch.

2.3.x is still alive, I belive :)

Thanks, KIR