- 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/XFileImporter.cpp

@@ -158,7 +158,7 @@ void XFileImporter::CreateDataRepresentationFromImport( aiScene* pScene, const X
 	{
 		pScene->mNumMaterials = 1;
 		// create the Material
-		Assimp::MaterialHelper* mat = new Assimp::MaterialHelper;
+		aiMaterial* mat = new aiMaterial;
 		int shadeMode = (int) aiShadingMode_Gouraud;
 		mat->AddProperty<int>( &shadeMode, 1, AI_MATKEY_SHADING_MODEL);
 		// material colours
@@ -567,7 +567,7 @@ void XFileImporter::ConvertMaterials( aiScene* pScene, const std::vector<XFile::
 		if( oldMat.mIsReference)
 			continue;
 
-		Assimp::MaterialHelper* mat = new Assimp::MaterialHelper;
+		aiMaterial* mat = new aiMaterial;
 		aiString name;
 		name.Set( oldMat.mName);
 		mat->AddProperty( &name, AI_MATKEY_NAME);