Config to disable basic_auth username checking

This can be confusing and/or annoying. (And I didn't really get what this block is used for anyways …)

My testinstall is protected via http-basic (so no one can hack my lazy-password of 123456), so I had to comment this block out before, getting conflicts everytime I did a `git branch` or `git pull` making me `git stash` everytime.

I've also seen some guys in #owncloud asking why their installation doesn't work with http-basic, telling them to comment out named block isn't really nice either.

@blizz @DeepDiver1975 @tanghus (?)
@karlitschek Should this be backported? This isn't a major bug, but pretty annoying, when this happens.