title: RStudio does not execute `system` commands from Rprofile.site
body: <p>Using Rstudio (Version 1.0.143) under Ubuntu (16.04), if I add <code>system("echo 'Hello world'")</code> to my <code>/usr/lib/R/etc/Rprofile.site</code> file, I have no Hello world message displayed in R studio at startup.<br>
  If I start R from the terminal I have the Hello world message.</p>
  
  <p>It seems that R studio ignores the <code>system</code> commands from <code>Rprofile.site</code> (idem from the <code>.Rprofile</code> file in the home directory)</p>
  
  <p>Is it possible to enable system commands executions or is there a good reason to avoid this behavior ?</p>