SYNOPSIS:
    MARKCG_FILL_NLC x y z target greylevel sigma sigmaw thresh

DESCRIPTION:
    Fill the connected area starting at x,y,z.
    All connected voxels belonging to the same set as x,y,z
    are remarked to targetset as long as the NLC threshold
    is not exceeded.
    Use -1 as greylevel to estimate it by a local gaussian blur.
    Use -2 as greylevel to estimate it by an inverted local
    gaussian blur.
