- 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/Q3DLoader.cpp

@@ -433,7 +433,7 @@ outer:
 
 		// Allocate a mesh and a material
 		aiMesh* mesh = pScene->mMeshes[real] = new aiMesh();
-		MaterialHelper* mat = new MaterialHelper();
+		aiMaterial* mat = new aiMaterial();
 		pScene->mMaterials[real] = mat;
 
 		mesh->mMaterialIndex = real;