Adding optional "index.html" file in /post/ID/ folder, for better SEO.

Tumblr doesn't discriminate by "slug" text. While it's not possible at the current time to do rule-based redirects on some hosts (such as GitHub Pages) ... this will at least prevent search-engines from stacking up a bunch of 404's checking that directory.

Unfortunately, there is still no way for hosts like GitHub Pages to do "catch-all" slug text, unlike Tumblr. So, people with messed up links to your blog that used to work will still return 404 unless they've simply left off the slug text.