title: ggplot error bars on a barplot have the wrong position
body: <p>When I generate the graph using the following code, the error bars are in strange positions.  Can you tell me how to get the error bars to show up around the top of each bar in the barchart?  I know this is basic, but I've been staring at it for hours now.  Thanks.</p>
  
  <pre><code>library(ggplot2)
  df &lt;- data.frame(gender=c("male","male","female","female"),
               trait=c("height","weight","height","weight"),
               value=c(70,150,65,120),
               sd = c(5,15,4,10))
  
  gg &lt;- ggplot(df,aes(x=trait,y=value,fill=trait))
  gg &lt;- gg+ geom_bar(stat="identity",position=position_dodge())
  gg &lt;- gg + facet_wrap(~ gender, ncol=1)
  
  limits &lt;- aes(ymax=df$value+df$sd, ymin=df$value-df$sd)                                                                                               
  gg &lt;- gg + geom_errorbar(limits)
  #gg &lt;- gg + geom_pointrange(limits)                                                                                                                                                                       
  gg
  </code></pre>