Add clf() to all plot demos. * axis.m, compass.m, contour3.m, contourf.m, cylinder.m, ellipsoid.m, errorbar.m, ezcontour.m, ezcontourf.m, ezmesh.m, ezmeshc.m, ezplot.m, ezplot3.m, ezpolar.m, ezsurf.m, ezsurfc.m, feather.m, fplot.m, loglogerr.m, pcolor.m, pie.m, pie3.m, plot3.m, plotmatrix.m, quiver.m, quiver3.m, refreshdata.m, ribbon.m, rose.m, scatter3.m, semilogx.m, semilogxerr.m, semilogy.m, semilogyerr.m, shading.m, sombrero.m, stairs.m, stem.m, stem3.m, surf.m, surfc.m, surfl.m, surfnorm.m, trimesh.m, triplot.m, trisurf.m, uimenu.m: Add clf() to the beginning of each demo to ensure pre-existing graphics objects don't interfere with the demo.

--- a/scripts/plot/surfl.m
+++ b/scripts/plot/surfl.m
@@ -179,6 +179,7 @@
 %! shading interp;
 
 %!demo
+%! clf
 %! [X,Y,Z]=sombrero;
 %! colormap(copper);
 %! [az, el] = view;