SUBROUTINE KFVXCV(IT, UPDATE, Z, VZ, CHISQ, LERROR)
C
C  >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
C   Refit a track to go near a "fuzzy" x,y,z point, that is a point
C   with a covariance matrix. The fit includes the covariance matrix
C   of the track as well as the vertex. The vertex is not updated.
C
C  IT      integer variable (read)
C          Number of the track to be fit
C
C  UPDATE  integer variable (read)
C          0 ==> do not update input track parameters (just calculate chisq)
C          1 ==> update input track parameters only
C          2 ==> update input track parameters & covariance matrices and
C                replace the original unconstrainted parameters by the
C                new ones. ****** This is a dangerous option. ******
C
C  Z       real array (read)
C          Point which the track must pass near
C
C  VZ      real array (read)
C          3x3 covariance matrix of Z
C
C *CHISQ   real variable (write)
C          Chisquare of fit
C
C *LERROR  logical variable (write)
C          TRUE if error
C  >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>