revert the Fl::check() removal in drawCurrentOpenglWindow: it breaks all GL2PS output...

Fltk/FlGui.cpp

@@ -63,10 +63,7 @@ class drawContextFltk : public drawContextGlobal{
     if(make_current) gl->make_current();
     gl->redraw();
     glFlush();
-    // drawCurrentOpenglWindow is currently only used when filling the pixel 
-    // buffer for bitmap image creation. To avoid spurious asynchronous gui 
-    // events fired while creating the picture, don't call check():
-    // FlGui::instance()->check();
+    FlGui::instance()->check();
   }
   int getFontIndex(const char *fontname)
   {