Switch to side-by-side view

--- a/src/qtgui/rclmain_w.h
+++ b/src/qtgui/rclmain_w.h
@@ -65,7 +65,7 @@
     virtual void enablePrevPage(bool);
     virtual void docExpand(int);
     virtual void ssearchAddTerm(QString);
-    virtual void startPreview(int docnum);
+    virtual void startPreview(int docnum, int);
     virtual void startNativeViewer(int docnum);
     virtual void previewNextInTab(int sid, int docnum);
     virtual void previewPrevInTab(int sid, int docnum);