demo2d.py exits without displaying NACA0012 grid

[stevenrhall]

When running demo2d.py, all the plots are shown, except for the NACA0012 grid. This might be an OS X issue only; however, it's easily fixed for all platforms by adding the line

pause(); print('')

right after the last occurrence of the line

fstats(p, t)

and right before the line

if __name__ == "__main__":

Without this additional line, the plot is made, but the python window with the drawing is immediately dismissed and so is never seen.