Do not kill the undo stack when doing a Save As...

The code does a reload on the buffer to avoid loose pointers if the
file changes directory. This commit adds a bool parameter to
Buffer::reload to allow for keeping the undo stack intact. This is of
couse only wanted in this case, not when reloading an earlier version
of the file.

src/Buffer.cpp

@@ -4580,7 +4580,7 @@ int Buffer::charCount(bool with_blanks) const
 }
 
 
-Buffer::ReadStatus Buffer::reload()
+Buffer::ReadStatus Buffer::reload(bool clearUndo)
 {
 	setBusy(true);
 	// c.f. bug http://www.lyx.org/trac/ticket/6587
@@ -4598,6 +4598,7 @@ Buffer::ReadStatus Buffer::reload()
 		updateTitles();
 		markClean();
 		message(bformat(_("Document %1$s reloaded."), disp_fn));
+		if (clearUndo)
 			d->undo_.clear();
 	} else {
 		message(bformat(_("Could not reload document %1$s."), disp_fn));

src/Buffer.h

@@ -225,7 +225,8 @@ public:
 	/// read a new document from a string
 	bool readString(std::string const &);
 	/// Reloads the LyX file
-	ReadStatus reload();
+	/// \param clearUndo if false, leave alone the undo stack.
+	ReadStatus reload(bool clearUndo = true);
 //FIXME: The following function should be private
 //private:
 	/// read the header, returns number of unknown tokens

src/frontends/qt4/GuiView.cpp

@@ -2320,7 +2320,7 @@ bool GuiView::renameBuffer(Buffer & b, docstring const & newname)
 
 	bool const saved = saveBuffer(b, fname);
 	if (saved)
-		b.reload();
+		b.reload(false);
 	return saved;
 }