Modify vmapExtractor to search for files in newer MPQs first.

Due to an ordering problem MPQ archives were being searched in reverse order.

A simple test showed that ~40k files were being loaded from less recent MPQ
archives.

I noticed this problem on mangos-classic when mmaps for BWL were incorrect. It turns out a pre-release version of BWL had been used, because the model was loaded from model.MPQ instead of patch.MPQ. This change fixed the problem.

Please check that this is correct for WotLK.