Overhaul use of __pltopt__.m to correctly check for cellstr, not just cell. * scripts/plot/private/__pltopt__.m: Use modern coding conventions. Eliminate unneeded input checking in subfunctions. Remove unused variables. * scripts/plot/contourf.m, scripts/plot/feather.m, scripts/plot/plotmatrix.m, scripts/plot/private/__bar__.m, scripts/plot/private/__quiver__.m, scripts/plot/private/__scatter__.m, scripts/plot/private/__stem__.m, scripts/plot/stairs.m: Use iscellstr, not iscell, to properly validate inputs to __pltopt__.

#include "mex.h"

void
mexFunction (int nlhs, mxArray* plhs[],
             int nrhs, const mxArray* prhs[])
{
  mwSize n;
  mwIndex i;

  if (nrhs != 1 || ! mxIsCell (prhs[0]))
    mexErrMsgTxt ("ARG1 must be a cell");

  n = mxGetNumberOfElements (prhs[0]);
  n = (n > nlhs ? nlhs : n);
  
  for (i = 0; i < n; i++)
    plhs[i] = mxDuplicateArray (mxGetCell (prhs[0], i));
}