ExternalRecorder: fix polling mode
Fix channel detection.

Use new request_channel_layout API

Fixes #12244
Have info and playback screen show proper number of channels
ExternalStreamHandler: Standardize log messages.
RingBuffer: Properly wait for readahead thread to start

Inverted test, no wait occurred causing a race condition later on which causes failures in LiveTV, usually when changing channels
RingBuffer: always read directly from file if read ahead thread isn’t running

readInternalMode can only work if the read ahead thread is running
HDHomeRun: Fix compilation on fedora 20