title: setting mfg in a multi plot prevents drawin on margin
body: <p>I'm trying to add common axes to a bunch of plots by putting them in the outer margin.
  Plots are drawn first in a loop (not in the example) then I wanted to draw axes on the bottom of the two rows of plots.</p>
  
  <p>But drawing the axis outside the plotting region is only possible without <code>mfg</code> being changed. How can I enable out-of-plot-drawing after changing <code>mfg</code>?</p>
  
  <pre><code>par(mfrow=c(2,2),
  mar=c(1,1,0,0),
  oma=c(3,0,0,0))
  
  #Some plots
  plot(function(x)x^2,from=-1,to=2,  frame.plot=T,axes=F)
  plot(function(x)x^3,from=-2,to=2,  frame.plot=T,axes=F)
  plot(rnorm(10),  frame.plot=T,axes=F)
  plot(1:10,       frame.plot=T,axes=F)
  # axis on last drawn plot (mfg=c(2,2)) - works
  axis(side=1,line=0,outer=TRUE)
  
  # set mfg to same value (mfg=c(2,2))
  par(mfg=c(2,2))
  
  # red axis is clipped to plot region, even with xpd?
  axis(side=1,line=-.2,outer=FALSE,xpd=NA,col="red")
  par(mfg=c(2,1))
  axis(side=1,line=-.2,outer=FALSE,xpd=NA,col="red")
  </code></pre>