void AddBSPFilesRecursively(VirtualSourceDir dir, Dictionary<string, string> systemDict, string projectDir)
{
if (dir.Files != null)
foreach (var fn in dir.Files)
{
string fullPath = VariableHelper.ExpandVariables(fn, systemDict);
_SourceFiles.Add(fullPath);
}
if (dir.Subdirs != null)
foreach (var subdir in dir.Subdirs)
AddBSPFilesRecursively(subdir, systemDict, projectDir);
}