Irrlicht mesh loader is now predicated on the proper preprocessor define (ASSIMP_BUILD_NO_IRRMESH_IMPORTER) as opposed to a similarly named but wrong define (ASSIMP_BUILD_NO_IRR_IMPORTER).
Irrlicht shared code is now excluded only if both the Irrlicht and Irrlicht Mesh importers are excluded from the build.
Merge pull request #145 from sherief/master

Fix for issue #114