compute_dircircularvariance

  COMPUTE_DIRCIRCULARVARIANCE
      CV = COMPUTE_DIRCIRCULARVARIANCE( ANGLES, RATES )

      Takes ANGLES in degrees. ANGLES and RATES should be
      row vectors.

  CV = 1 - |R|
  R = (RATES * EXP(I*ANGLES)') / SUM(RATES)

  See Ringach et al. J.Neurosci. 2002 22:5639-5651