Switch to side-by-side view

--- a/src/qtgui/rclmain_w.h
+++ b/src/qtgui/rclmain_w.h
@@ -96,6 +96,7 @@
     virtual void previewPrevInTab(int sid, int docnum);
     virtual void previewExposed(int sid, int docnum);
     virtual void resetSearch();
+    virtual void eraseDocHistory();
 protected:
     virtual void closeEvent( QCloseEvent * );