* The default channel mask for mono files was 0x0001 (front left) but it
  makes more sense to use 0x0004 (front center) for such files.

* Also FLAC will accept not only mono WAV files with 0x0001 mask, but also
  with 0x0002 (requested at https://sourceforge.net/p/flac/bugs/390/)
  and 0x0004 (e.g. SoX creates mono files with this mask).

* The comment about channel support was updated.

* The error message
     "Use --channel-map=none option to store channels in current order; FLAC files
     must also be decoded with --channel-map=none to restore correct order."
  is misleading: FLAC never changes the order of channels.
  Decoding with this options also sets the channel mask of the resulting WAV
  file to 0. Without this option the mask is equal to the value of
  WAVEFORMATEXTENSIBLE_CHANNEL_MASK tag.

Patch-from: lvqcl <lvqcl.mail@gmail.com>