Include last_plotcmd state inside each object as well as in the global.
document last_plotcmd change
Reset before every plot, unless it's a multiplot or a replot.  That clears up
things like persistent axis labels.  It isn't quite perfect, since multiplots
still suffer the same problem - but it avoids the need to manually unset
every plot option that we set.
fix issue with m*tics
fixed issue with Y2 axis usage/documentation not agreeing