title: cSplit library(splitstackshape) is always dropping the column
body: <p>I was searching for a way to split the column content by a separator and converting a table into a long format. I found <code>cSplit</code> from the <code>splitstackshape</code> package and it is almost doing what I was looking for.</p>
  
  <p>Problem is now with the <code>drop</code> option. I expected my split column to be copied in a way, but this does not happen. Am I doing it wrong? Somebody experienced the problem?</p>
  
  <p>I am not sure if I do something wrong, but the <code>drop = FALSE</code> option is not working in my case.</p>
  
  <p>Here is an example:</p>
  
  <pre><code>library(splitstackshape)
  jnk &lt;- data.table(a = '1,2,3,4,5', b = 5)
  jnk
  #            a b
  # 1: 1,2,3,4,5 5
  
  cSplit(jnk, 'a', ',', 'long', drop = FALSE)
  #    a b
  # 1: 1 5
  # 2: 2 5
  # 3: 3 5
  # 4: 4 5
  # 5: 5 5
  </code></pre>
  
  <p>What I expected was something like this:</p>
  
  <pre><code>cSplit(jnk, 'a', ',', 'long', drop = FALSE)
  #    a b    a.orig
  # 1: 1 5 1,2,3,4,5
  # 2: 2 5 1,2,3,4,5
  # 3: 3 5 1,2,3,4,5
  # 4: 4 5 1,2,3,4,5
  # 5: 5 5 1,2,3,4,5
  </code></pre>
  
  <p>I am using version 1.4.2</p>