Applied old InfraWorks patches to current AssImp

This branch applies the AssImp changes that we did in the past based on AssImp SVN revision 1100. 
The source of these changes is the SVN patch file current_version.patch in <IW>/Desktop/3rdParty/AssImp

Note: 
One of the changes had not been adopted: For some files, the original M3Importer had wrongly returned true and avoided other importers from being tried. In the latest version, the M3Importer doesn't exist anymore anyway.

It's not fully clear to me if/whether the latest version of AssImp can still load M3 files. According to the format list, it does. If any user ever actually complains about not loading StarCraft models anymore, we might have a look.