[new exporter]: LaTeX output from babel escapes comment delimiter

[Michael Gauland <mikelygee@no8wireless.co.nz>]

I use the xtables package in R to generate nice-looking tables for LaTeX output,
as in the snippet below. The new exporter escapes the % symbol in the R output,
so that the comments generated by xtable are no longer comments. 

* Snippet
  #+HEADER: :results output latex
  #+HEADER: :exports results
  #+BEGIN_SRC R
  library(xtable)
  xtable(matrix(c(1,2,3,4),nrow=2,ncol=2))
  #+END_SRC

  #+RESULTS:
  #+BEGIN_LaTeX
  % latex table generated in R 2.15.1 by xtable 1.7-0 package
  % Thu Oct 25 13:11:30 2012
  \begin{table}[ht]
  \begin{center}
  \begin{tabular}{rrr}
    \hline
   & 1 & 2 \\ 
    \hline
  1 & 1.00 & 3.00 \\ 
    2 & 2.00 & 4.00 \\ 
     \hline
  \end{tabular}
  \end{center}
  \end{table}
  #+END_LaTeX