title: Plot() error when using REngine.Rserve
body: <p>I'm now work on a project which wants to use org.rosuda.REngine.Rserve to use facilities of R by C#. I have a particular problem that when I run the following code in C# client side:</p>
  
  <pre><code>c.eval("pdf(file=\"plots.pdf\", width=11, height=8.5)");
  c.eval("plot(1,2)");
  </code></pre>
  
  <p>An error occour which said</p>
  
  <pre><code>Error in plot.new():cannot open file '', reason No such file or directory
  </code></pre>
  
  <p>But I checked that the file "plots.pdf" has already been created successfully by "pdf.." function. In R semantics, the successive plot() will output figure to the active device opened by the "pdf(...)" function, i.e. "plots.pdf" this time. But I'm very confused that why the error indicated that the file is ''.
  I use R-2.15.0 and Rserve-1.7.0 in linux server side. 
  I'm eager to see your response.
  Thanks a lot.</p>