- extract MaterialHelper and move all of its members to aiMaterial in /include.

- pull in IOhannes' patch to set the gcc default visibility for all symbols to NO and to mark ASSIMP_API with __attribute__ ((visibility("default"))).
- drop unneeded ASSIMP_API from most internal classes in /code, we just need to keep some exports on Windows to keep AssimpView alive.

git-svn-id: https://assimp.svn.sourceforge.net/svnroot/assimp/trunk@1066 67173fc5-114c-0410-ac8e-9d2fd5bffc1f

code/NFFLoader.cpp

@@ -1195,7 +1195,7 @@ void NFFImporter::InternReadFile( const std::string& pFile,
 		}
 
 		// generate a material for the mesh
-		MaterialHelper* pcMat = (MaterialHelper*)(pScene->mMaterials[m] = new MaterialHelper());
+		aiMaterial* pcMat = (aiMaterial*)(pScene->mMaterials[m] = new aiMaterial());
 
 		mesh->mMaterialIndex = m++;