TOC containing files (structural files in source code terms) always rewritten

[Maetveis]

#81 Added incremental generation to most rst outputs, but
the rst files for namespace lists, filelists etc. are always written to, even if their content wouldn't change. This triggers sphinx to re-read and build them each time.

There is only a small fixed number of these files, so it not as beneficial to skip these as it was for the other html wrappers, but it would be nice to reach true noop builds when nothing changed.