- 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/STLLoader.cpp

@@ -143,7 +143,7 @@ void STLImporter::InternReadFile( const std::string& pFile,
 	}
 
 	// create a single default material - everything white, as we have vertex colors
-	MaterialHelper* pcMat = new MaterialHelper();
+	aiMaterial* pcMat = new aiMaterial();
 	aiString s;
 	s.Set(AI_DEFAULT_MATERIAL_NAME);
 	pcMat->AddProperty(&s, AI_MATKEY_NAME);