title: Highlight significant coefficients in coefplot
body: <p>Is there a way of changing the colour, to red say, of <em>only</em> significant coefficients on the <code>coefplot</code> plot?</p>
  
  <p>For example (plot 2 in coefplot's helpfile), </p>
  
  <pre><code>require(coefplot)
  y1 &lt;- rnorm(1000,50,23)
  y2 &lt;- rbinom(1000,1,prob=0.72)
  x1 &lt;- rnorm(1000,50,2) 
  x2 &lt;- rbinom(1000,1,prob=0.63) 
  x3 &lt;- rpois(1000, 2) 
  x4 &lt;- runif(1000,40,100) 
  x5 &lt;- rbeta(1000,2,2) 
  
  longnames &lt;- c("a long name01","a long name02","a long name03",
                 "a long name04","a long name05")
  
  fit1 &lt;- lm(y1 ~ x1 + x2 + x3 + x4 + x5)
  
  # plot 2
  longnames &lt;- c("(Intercept)", longnames) 
  coefplot(fit1, longnames, intercept=TRUE)
  </code></pre>