optionally (use_lpc=2) support Cholesky factorization for finding the lpc coeficients

optionally (use_lpc=2) support Cholesky factorization for finding the lpc coeficients
  this will find the coefficients which minimize the sum of the squared errors,
  levinson-durbin recursion OTOH is only strictly correct if the autocorrelation matrix is a
  toeplitz matrix which it is only if the blocksize is infinite, this is also why applying
  a window (like the welch winodw we currently use) improves the lpc coefficients generated
  by levinson-durbin recursion ...

optionally (use_lpc>2) support iterative linear least abs() solver using cholesky
  factorization with adjusted weights in each iteration

compression gain for both is small, and multiple passes are of course dead slow

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@5747 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b