load_other_extensions=False in ExtensionApp

[davidbrochart]

I don't understand how an ExtensionApp is supposed to work when it has load_other_extensions=False. Isn't it going to prevent loading itself also when launched directly?
In the simple_ext1 example, if you set this line to False, then python -m simple_ext1 will show a 404 error in the browser.

[Zsailer]

Good catch. This is a bug.

Looks like this was dropped in #180 by accident. I'll work on a fix + some tests today.