title: Issue with quantmod add_TA and chart_Series - lines and text disappear after next add_TA is called
body: <p>I am using new <code>chart_Series</code> and <code>add_TA</code> quite a lot. It works very well for me and I find it very useful.</p>
  
  <p>I am trying to add a few things (horizontal lines and some text) on a graph. Here problems start to occur. After horizontal lines and text are drawn correctly they disappear if I call subsequent <code>add_TA</code>... Please see the example code below which reproduces the problem:</p>
  
  <pre><code>library(quantmod)
  
  getSymbols("SPY")
  
  dev.new()
  chart_Series(SPY)
  add_TA(ADX(HLC(SPY))$ADX)
  abline(h=15, col="red")
  abline(h=35, col="green")
  text(10, 7, "Text and horizontal lines disappear after next add_TA is called",
    col="blue", cex=0.8, adj = c(0,0))
  # run the code up to this point (including text(...
  # see how horizontal lines drawn with abline and text is displayed correctly
  # now run the last line by adding additional TA and you will see that lines
  # and text disappears
  add_TA(DVI(Cl(SPY))$dvi)
  </code></pre>
  
  <p>Is this intended behavior?</p>
  
  <p>EDIT: How to make this work (as per Joshua comment below: redrawing also line and text when plot object (chob) is being redrawn)?</p>