Update read_ptv_is_files.m

I belie the change(in line 54) is due to the updated MATLAB
Update plot_long_trajectories.m

all the xf,yf,zf were converted to x,y,z.I believe this is also due to the updated MATLAB
Merge pull request #1 from jimmy516/master

Update the post-processing MATLAB function by Dr.Liberzon