title: simultaneous download using download.file
body: <p>Since the version 3.2.1, the <a href="http://cran.r-project.org/doc/manuals/r-patched/NEWS.pdf">official</a> R document says that there is support for simultaneous downloads. Following is the quoted text from help file: </p>
  
  <p><em>Support for method "libcurl" is optional: use capabilities("libcurl") to see if it is supported on your build. It provides (non-blocking) access to https:// and ftps:// URLs. There is support for simultaneous downloads, so url and destfile can be character vectors of the same length greater than one. For a single URL and quiet = FALSE there a progress bar is shown in interactive use.</em></p>
  
  <p>But when I tried to download two files from two different websites, it downloaded only one: </p>
  
  <pre><code>url_list&lt;-c("http://cran.r-project.org/doc/manuals/r-patched/R-exts.html","http://cran.r-project.org/doc/manuals/r-patched/NEWS.pdf")
  dest_list&lt;-c("test1.html","test2.pdf")
  download.file(url_list,dest_list)
  
  trying URL 'http://cran.r-project.org/doc/manuals/r-patched/R-exts.html'
  Content type 'text/html' length 874175 bytes (853 KB)
  downloaded 853 KB
  
  Warning messages:
  1: In download.file(url_list, dest_list) :
    only first element of 'url' argument used
  2: In download.file(url_list, dest_list) :
    only first element of 'destfile' argument used
  </code></pre>
  
  <p>Then, I saw that I missed using an argument <code>method="libcurl"</code></p>
  
  <pre><code>download.file(url_list,dest_list,method="libcurl"). 
  </code></pre>
  
  <p>Once I run this command in RStudio: R Studio gives fatal warning and R session gets aborted. With the R for Windows GUI, the following warning occurs (and then shut down): </p>
  
  <p><em>R for Windows GUI front-end has stopped working. 
  "A problem caused the program to stop working correctly. windows will close the program and notify you if a solution is available.".</em> </p>
  
  <p>I am using Windows 8.0. I also ran <code>capabilities("libcurl")</code> and it gives the following output. </p>
  
  <pre><code>libcurl 
     TRUE
  </code></pre>