* browsed through all code files starting with A to F and added non-blocking intf_Use...

* browsed through all code files starting with A to F and added non-blocking intf_UserFatal calls next to msg_err where I think that it is necessary.
I tried to select the most important msg_errs. If I missed your favourite, feel free to add it.
Feedback on the wording and the placement of the interaction calls is strongly welcomed.

For the records: I'm using some general topics for most of the dialogues to produce less work for the translators. The current ones go like this:
"Audio output failed", "Network interaction failed", "Streaming / Transcoding failed", "Audio filtering failed", "File reading failed", "Playback failure"

More to come.