First use of "trusted" xattr namespace

[pjotrek-b]

Until now, I've only used the user namespace for xattrs.
I've now tested the trusted namespace, and found out this:

1. You may read/write only as root.
2. It co-exists nicely with user.

This makes whole new use-cases possible, and gives the ability to have "serious attributes" parallel to "regular ones".

I'm using this thread here to track notes on the matter.