title: R fwrite separates a dataframe entry that has commas
body: <p>I am thinking of using <code>fwrite</code> from the development version of data.table to write large dataframes to <code>csv</code> files fast. However, it seems to separate whatever goes after a comma into a separate column (not desired) while <code>write.csv</code> does not do that (as desired). Here is an example.</p>
  
  <pre><code># Install data.table 1.9.7
  remove.packages("data.table")                         # First remove the current version
  install.packages("data.table", type = "source",
      repos = "http://Rdatatable.github.io/data.table") # Then install devel version
  
  library(data.table)
  x &lt;- c('a1, b1, c1', 'a2, b2, c2')
  y &lt;- c(1, 2)
  df &lt;- data.frame(x, y)
  fwrite(df, 'fwrite.csv')
  write.csv(df, 'write.csv')
  </code></pre>
  
  <p>If you look at the file written by <code>fwrite</code>, you will see the b's and c's are separated into separate columns (not desired) while that does not happen in the file written by <code>write.csv</code> (as desired). Does anyone know how to help <code>fwrite</code> not do that? Thank you.</p>