* ext/audiofile.m(ca_audio_file_initialize): now open AudioFile in read mode,   AudioStreamBasicDescription(cf sample rate, channel number) are derived from   opened file, and :rate and :channel option's default values are set by them.   And in read mode, :format option is not necessary and ignored.
* ext/audiofile.m(ca_audio_file_initialize): now open AudioFile in read mode,
  AudioStreamBasicDescription(cf sample rate, channel number) are derived from
  opened file, and :rate and :channel option's default values are set by them.
  And in read mode, :format option is not necessary and ignored.

nagachika/ruby-coreaudio,nagachika/ruby-coreaudio