Clear undo/redo stack when reloading buffer. This fixes #7208.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@37155 a592a061-630c-0410-9148-cb99ea01b6c8

src/Buffer.cpp

@@ -4250,6 +4250,7 @@ Buffer::ReadStatus Buffer::reload()
 		updateTitles();
 		markClean();
 		message(bformat(_("Document %1$s reloaded."), disp_fn));
+		d->undo_.clear();
 	} else {
 		message(bformat(_("Could not reload document %1$s."), disp_fn));
 	}	

src/Undo.cpp

@@ -241,6 +241,16 @@ Undo::~Undo()
 }
 
 
+void Undo::clear()
+{
+	d->undostack_.clear();
+	d->redostack_.clear();
+	d->undo_finished_ = true;
+	d->group_id = 0;
+	d->group_level;
+}
+
+
 bool Undo::hasUndoStack() const
 {
 	return !d->undostack_.empty();

src/Undo.h

@@ -53,6 +53,9 @@ public:
 
 	~Undo();
 
+	/// Clear out all undo/redo contents.
+	void clear();
+
 	/// this will undo the last action - returns false if no undo possible
 	bool textUndo(DocIterator &);