title: SSL verification causes RCurl and httr to break - on a website that should be legit
body: <p>i'm trying to automate the login of the UK's data archive service.  that website is obviously trustworthy.  unfortunately, both <code>RCurl</code> and <code>httr</code> break at SSL verification.  my web browser doesn't give any sort of warning.  i can work around the issue by using <code>ssl.verifypeer = FALSE</code> in <code>RCurl</code> but i'd like to understand what's going on?</p>
  
  <pre><code># breaks
  library(httr)
  GET( "https://www.esds.ac.uk/secure/UKDSRegister_start.asp" )
  
  # breaks
  library(RCurl)
  cert &lt;- system.file("CurlSSL/cacert.pem", package = "RCurl")
  getURL("https://www.esds.ac.uk/secure/UKDSRegister_start.asp",cainfo = cert)
  
  # works
  library(RCurl)
  getURL(
      "https://www.esds.ac.uk/secure/UKDSRegister_start.asp" , 
      .opts = list(ssl.verifypeer = FALSE)
  ) # note: use list(ssl.verifypeer = FALSE,followlocation=TRUE) to see content
  </code></pre>