Switch to side-by-side view

--- a/src/qtgui/rclmain_w.h
+++ b/src/qtgui/rclmain_w.h
@@ -88,6 +88,7 @@
     virtual void docExpand(int);
     virtual void ssearchAddTerm(QString);
     virtual void startPreview(int docnum, int);
+    virtual void startPreview(Rcl::Doc doc);
     virtual void startNativeViewer(int docnum);
     virtual void previewNextInTab(int sid, int docnum);
     virtual void previewPrevInTab(int sid, int docnum);