title: gdkCursorNewFromPixmap example error
body: <p>The example code from <code>gdkCursorNewFromPixmap</code> causes an error on Ubuntu with R 2.14.1 and <code>RGtk2</code> 2.20.25</p>
  
  <p>Code:</p>
  
  <pre><code>library(RGtk2)
  
  # This data is in X bitmap format, and can be created with the 'bitmap' utility in X11
  cursor1_width &lt;- 16
  cursor1_height &lt;- 16
  cursor1_bits &lt;- c(
    0x80, 0x01, 0x40, 0x02, 0x20, 0x04, 0x10, 0x08, 0x08, 0x10, 0x04, 0x20,
    0x82, 0x41, 0x41, 0x82, 0x41, 0x82, 0x82, 0x41, 0x04, 0x20, 0x08, 0x10,
    0x10, 0x08, 0x20, 0x04, 0x40, 0x02, 0x80, 0x01)
  cursor1mask_bits &lt;- c(
    0x80, 0x01, 0xc0, 0x03, 0x60, 0x06, 0x30, 0x0c, 0x18, 0x18, 0x8c, 0x31,
    0xc6, 0x63, 0x63, 0xc6, 0x63, 0xc6, 0xc6, 0x63, 0x8c, 0x31, 0x18, 0x18,
    0x30, 0x0c, 0x60, 0x06, 0xc0, 0x03, 0x80, 0x01)
   fg &lt;- c(65535, 0, 0) # Red.
   bg &lt;- c(0, 0, 65535) # Blue.
   source &lt;- gdkPixmapNew(NULL, cursor1_width, cursor1_height, 8) 
   mask &lt;- gdkPixmapNew(NULL, cursor1_width, cursor1_height, 8) 
   cursor &lt;- gdkCursorNewFromPixmap(source, mask, fg, bg,0,0 )
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>Error in checkPtrType(source, "GdkPixmap") : 
    object of class GdkBitmap, RGtkObject isn't a GdkPixmap
  Calls: gdkCursorNewFromPixmap -&gt; checkPtrType
  </code></pre>